The empty String madness (2023)


When we submit a HTML form with empty input fields which are bound to non-primitive bean properties, we'd rather like to keep them null instead of being polluted with empty strings or zeroes. This is very significant as to validation constraints such as @NotNull in Bean Validation and NOT NULL in relational databases. Across years and JSF/EL versions this turned out to be troublesome as not anyone agreed on each other. I sometimes even got momentarily confused myself when it would work and when not. I can imagine that a lot of other JSF developers have the same feeling. So let's do some digging in history and list all the facts and milestones in one place for best overview, along with an useful summary table with the correct solutions.

JSF 1.0/1.1 (2004-2006)

Due to the nature of HTTP, empty input fields arrive as empty strings instead of null. The underlying servlet request.getParameter(name) call returns an empty string on empty input fields. Nothing to do against, that's just how HTTP and Servlets work. A value of null represents the complete absence of the request parameter, which is also very significant (e.g. the servlet could this way check if a certain form button is pressed or not, irrespective of its value/label which could be i18n'ed). So we can't fix this in HTTP/Servlet side and have to do it in MVC framework's side. To avoid the model being polluted with empty strings, you would in JSF 1.0/1.1 need to create a custom Converter like below which you explicitly register on the inputs tied to java.lang.String typed model value.

public class EmptyToNullStringConverter implements Converter { @Override public Object getAsObject(FacesContext facesContext, UIComponent component, String submittedValue) { if (submittedValue == null || submittedValue.isEmpty()) { if (component instanceof EditableValueHolder) { ((EditableValueHolder) component).setSubmittedValue(null); } return null; } return submittedValue; } @Override public String getAsString(FacesContext facesContext, UIComponent component, Object modelValue) { return (modelValue == null) ? "" : modelValue.toString(); }}

Which is registered in faces-config.xml as below:

<converter> <converter-id>emptyToNull</converter-id> <converter-class>com.example.EmptyToNullStringConverter</converter-class></converter>

And used as below:

<h:inputText value="#{bean.string1}" converter="emptyToNull" /><h:inputText value="#{bean.string2}" converter="emptyToNull" /><h:inputText value="#{bean.string3}" converter="emptyToNull" />

The converter-for-class was not supported on java.lang.String until JSF 1.2.

The non-primitive numbers wasn't a problem in JSF 1.x, but only in specific server/EL versions. See later.

JSF 1.2 (2006-2009)

Since JSF 1.2, the converter-for-class finally supports java.lang.String (see also spec issue 131). So you can simply register the above converter as below and it'll get automatically applied on all inputs tied to java.lang.String typed model value.

<converter> <converter-for-class>java.lang.String</converter-for-class> <converter-class>com.example.EmptyToNullStringConverter</converter-class></converter>
<h:inputText value="#{bean.string1}" /><h:inputText value="#{bean.string2}" /><h:inputText value="#{bean.string3}" />

Tomcat 6.0.16 - 7.0.x (2007-2009)

Someone reported Tomcat issue 42385 wherein EL failed to set an empty String value representing an integer into a primitive int bean property. This uncovered a long time RI bug which violated section 1.18.3 of EL 2.1 specification.

1.18.3 Coerce A to Number type N

  • If A is null or "", return 0.
  • ...

In other words, when the model type is a number, and the submitted value is an empty string or null, then EL should coerce all integer based numbers int, long, Integer, Long and BigInteger to 0 (zero) before setting the model value. The same applies to decimal based numbers float, double, Float, Double and BigDecimal, which will then be coerced to 0.0. This was not done rightly in Oracle (Sun) nor in Apache EL implementations at the date. They both just set null in the number/decimal typed model value and only Apache EL failed on primitives whereas Oracle EL properly set the default value of zero (and hence that Tomcat issue report).

Since Tomcat 6.0.16, Apache EL started to set all number/decimal typed model values with 0 and 0.0 respectively. That's okay for primitive types like int, long, float and double, but that's absolutely not okay for non-primitive types like Integer, Long, Float, Double, BigInteger and BigDecimal. They should stay null when the submitted value is empty or null. The same applies to Boolean fields which got a default value of false and Character fields which got a default value of \u0000.

So I created JSP spec issue 184 for that (EL was then still part of JSP). This coercion doesn't make sense for non-primitives. The issue got a lot of recognition and votes.After complaints from JSF users, since Tomcat 6.0.17 a new VM argument was added to disable this Apache EL behavior on non-primitive number/decimal types.


It became the most famous Tomcat-specific setting among JSF developers. It even worked in JBoss and all other servers using Apache EL parser (WebSphere a.o). It could even be set programmatically with help of a ServletContextListener.

@WebListenerpublic class Config implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent event) { System.setProperty("org.apache.el.parser.COERCE_TO_ZERO", "false"); } @Override public void contextDestroyed(ServletContextEvent event) { // NOOP. }}

JSF 2.x (2009-current)

To reduce the EmptyToNullStringConverter boilerplate, JSF 2.0 introduced a new context param with a rather long name which should achieve exactly the desired behavior of interpreting empty string submitted values as null.

<context-param> <param-name>javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL</param-name> <param-value>true</param-value></context-param>

To avoid non-primitive number/decimal typed model values being set with zeroes, on Tomcat and clones you still need the VM argument for the Apache EL parser as explained in the previous section. See also a.o. the Communication in JSF 2.0 article here.

EL 3.0 (2013-current)

And then EL 3.0 was introduced as part of Java EE 7 (which also covers JSF 2.2). With this version, the aforementioned JSP spec issue 184 was finally fixed. EL specification does no longer require to coerce non-primitive number/decimal types to zero. Apache EL parser was fixed in this regard. The -Dorg.apache.el.parser.COERCE_TO_ZERO=false is now the default behavior and the VM argument became superflous.

However, the EL guys went a bit overboard with fixing issue 184. They also treated java.lang.String the same way as a primitive! See also section 1.23.1 and 1.23.2 of EL 3.0 specification (emphasis mine):

1.23.1 To Coerce a Value X to Type Y

  • If X is null and Y is not a primitive type and also not a String, return null.
  • ...

1.23.2 Coerce A to String

  • If A is null: return “”
  • ...

They didn't seem to realize that coercion can work in two ways: when performing a "get" and when performing a "set". Coercion from null string to empty string makes definitely sense during invoking the getter (you don't want to see "null" being printed over all place in HTML output, right?). Only, it really doesn't make sense during invoking the setter (as the model would be polluted with empty strings over all place).

And suddenly, the javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL didn't have any effect anymore. Even when JSF changes the empty string submitted value to null as instructed, EL 3.0 will afterwards coerce the null string back to empty string again right before invoking the model value setter. This was first noticeable in Oracle EL (WildFly, GlassFish, etc) and only later in Apache EL (see next chapter). This was discussed in JSF spec issue 1203 and Mojarra issue 3075, and finally EL spec issue 18 was created to point out this mistake in EL 3.0.

Until they fix it, this could be workarounded with a custom ELResolver for common property type of java.lang.String like below which utilizes the new EL 3.0 introduced ELResolver#convertToType() method. The remainder of the methods is not relevant.

public class EmptyToNullStringELResolver extends ELResolver { @Override public Class<?> getCommonPropertyType(ELContext context, Object base) { return String.class; } @Override public Object convertToType(ELContext context, Object value, Class<?> targetType) { if (value == null && targetType == String.class) { context.setPropertyResolved(true); } return value; } @Override public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base) { return null; } @Override public Class<?> getType(ELContext context, Object base, Object property) { return null; } @Override public Object getValue(ELContext context, Object base, Object property) { return null; } @Override public boolean isReadOnly(ELContext context, Object base, Object property) { return true; } @Override public void setValue(ELContext context, Object base, Object property, Object value) { // NOOP. }}

Which is registered in faces-config.xml as below:

<application> <el-resolver>com.example.EmptyToNullStringELResolver</el-resolver></application>

This was finally fixed in Oracle EL 3.0.1-b05 (July 2014). It is shipped as part of a.o. GlassFish 4.1 and WildFly 8.2. So the above custom ELResolver is unnecessary on those servers. Do note that you still need to keep The Context Param With The Long Name in EL 3.0 reagardless of the fix and the custom ELResolver!

Tomcat 8.0.7 - 8.0.15 (2014)

Apache EL 3.0 worked flawlessly until someone reported Tomcat issue 56522 that it didn't comply the new EL 3.0 requirement of coercing null string to empty string, even though that new requirement didn't make sense. So since Tomcat 8.0.7, Apache EL also suffered from this EL 3.0 problem of unnecessarily coercing null string to empty string during setting the model value. However, the above EmptyToNullStringELResolver workaround in turn still failed in all Tomcat versions until 8.0.15, because it didn't take any custom ELResolver into account. See also Tomcat issue 57309. This was fixed in Tomcat 8.0.16.

If upgrading to at least Tomcat 8.0.16 in order to utilize the EmptyToNullStringELResolver is not an option, the only way to get it to work is to replace Apache EL by Oracle EL in Tomcat-targeted JSF web applications. This can be achieved by dropping the current latest release in webapp's /WEB-INF/lib (which is javax.el-3.0.1-b08.jar at the time of writing) and adding the below context parameter to web.xml to tell Mojarra to use that EL implementation instead:

<context-param> <param-name>com.sun.faces.expressionFactory</param-name> <param-value>com.sun.el.ExpressionFactoryImpl</param-value></context-param>

Or when you're using MyFaces:

<context-param> <param-name>org.apache.myfaces.EXPRESSION_FACTORY</param-name> <param-value>com.sun.el.ExpressionFactoryImpl</param-value></context-param>

Of course, this is also a good alternative to the custom EmptyToNullStringELResolver in its entirety. Also here, you still need to keep The Context Param With The Long Name.


Here's a summary table which should help you in figuring out what to do in order to keep non-primitive bean properties null when the submitted value is empty or null (so, to avoid pollution of model with empty strings or zeroes over all place).

Note: Tomcat and JBoss use Apache EL, and GlassFish and WildFly use Oracle EL. Other servers (mainly the closed source ones such as WebSphere, WebLogic, etc) are not covered as I can't tell the exact versions being affected, but generally the same rules apply depending on the EL implementation being used.

JSFTomcatJBoss ASWildFlyGlassFish
  • MC: manually register EmptyToNullStringConverter over all place in <h:inputXxx converter>.
  • AC: automatically register EmptyToNullStringConverter on java.lang.String class.
  • UT: upgrade Tomcat to at least 6.0.17 as version 6.0.16 introduced the broken behavior on non-primitive number/decimal types and the VM argument was only added in 6.0.17.
  • CZ: add -Dorg.apache.el.parser.COERCE_TO_ZERO=false VM argument.
  • JF: add javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL=true context param.
  • JK: add jakarta.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL=true context param.
  • JK*: add jakarta.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL=true context param, and when using Mojarra, use a minimum of 3.0.4 and 4.0.1; for older versions you need a EmptyToNullStringELResolver.
  • ER: register EmptyToNullStringELResolver, or alternatively, just do UE.
  • UE: migrate/upgrade to Oracle EL implementation version 3.0.1-b05 or newer.
  • : this JSF version is not supported on this server anyway.


Is it better to use null or empty string? ›

An empty string is useful when the data comes from multiple resources. NULL is used when some fields are optional, and the data is unknown.

Is Epsilon the empty string? ›

In formal treatments, the empty string is denoted with ε or sometimes Λ or λ. The empty string should not be confused with the empty language ∅, which is a formal language (i.e. a set of strings) that contains no strings, not even the empty string. The empty string has several properties: |ε| = 0.

How to pass an empty string in Java? ›

Java String isEmpty() Method Example 2
  1. public class IsEmptyExample2 {
  2. public static void main(String[] args) {
  3. String s1="";
  4. String s2="Javatpoint";
  5. // Either length is zero or isEmpty is true.
  6. if(s1.length()==0 || s1.isEmpty())
  7. System.out.println("String s1 is empty");
  8. else System.out.println("s1");

How to pass empty string in SQL? ›

In Oracle, if you insert an empty string ('') to a NUMBER column, Oracle inserts NULL. In SQL Server, if you insert an empty string ('') to an integer column (INT i.e.), SQL Server inserts 0, if you insert an empty string to a decimal column (DECIMAL i.e.), the statement fails.

Why is using null bad? ›

Null is a special instruction in the language that can substitute any type. Put in another way; it means that null inherits from all reference types. Because of that, you cannot think of your code logically anymore. You always have to check if the value is of subtype null or not.

Is it better to return null or empty object? ›

It is best practice to return empty values rather than null ones. Especially when you return a collection, enumerable, or an object, you should avoid returning null. Returning null is okay if your code handles the returning null value. But developers may forget to write a null check.

Is the empty string always in Sigma Star? ›

Now, by definition, Σ∗ is the set of all finite strings that can be written using the characters of Σ. This always includes the empty string ϵ and, as long as Σ≠∅, it also contains strings of all finite lengths. So the claim in the question that Σ∗={e,0,1,01,10} is incorrect: Σ∗ is an infinite set.

What is the code for empty string? ›

An empty string is represented as "" . It is a character sequence of zero characters. A null string is represented by null . It can be described as the absence of a string instance.

What is ε called? ›

Greek Alphabet
20 more rows

What does string null mean? ›

A string is null if it has not been assigned a value (in C++ and Visual Basic) or if it has explicitly been assigned a value of null . Although the composite formatting feature can gracefully handle a null string, as the following example shows, attempting to call one if its members throws a NullReferenceException.

How do you check if a string is null? ›

  1. Get the String to be checked in str.
  2. We can simply compare the string with Null using == relational operator. Syntax: if(str == null)
  3. Print true if the above condition is true. Else print false.
Jan 22, 2020

What is the difference between isEmpty and isBlank? ›

The isEmpty operator checks if a string contains no characters and is only whitespace. The isBlank operator checks if a string contains no characters, is only whitespace, and is null.

How do you handle NULL values? ›

Putting the median or mean of the whole column was the simple approach. But I like a bit more specific approach to the median and mean. Instead of taking the median of the whole age column and filling up all the null values, filling up the null values using the mean age of each pclass and 'alive' will be more accurate.

How do you take an empty string? ›

Java String isEmpty() Method

The isEmpty() method checks whether a string is empty or not. This method returns true if the string is empty (length() is 0), and false if not.

What is the difference between blank and NULL? ›

The fundamental difference between these two is that null controls the validation at the database level, and blank is used during form field validation at the application level.

What is the billion dollar mistake? ›

Speaking at a software conference in 2009, Tony Hoare apologized for inventing the null reference: I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W).

Why null is a billion dollar mistake? ›

The excuse. We, as developers, use null because it is easy (to write down) and because we believe it improves the efficiency of our software. By making this mistake we ignore that the code is read up to 10 times more than it is written. Reading code with nulls is more arduous and difficult.

What can I use instead of null? ›

Empty String

String data types are often initalized to null as well. However, for the exact same reasons, we prefer to use an empty string to replace null .

Is returning null a bad practice? ›

It's very tempting to just return a null reference, but this could cause problems for the caller. If the caller(or callers), fails to do a null check, it could result in a NullPointerException being thrown if some value from the item object is used.

Does null consume memory? ›

"In Java, null is just a value that a reference (which is basically a restricted pointer) can have. It means that the reference refers to nothing. In this case you still consume the space for the reference. This is 4 bytes on 32-bit systems or 8 bytes on 64-bit systems.

Do NULLs take up space? ›

One common misconception about NULL values is that they represent “nothing” or “no value.” NULLs are indeed a value. They take up space on your database hard drive as opposed to “nothing” that indicates there is no value.

Is Sigma Star infinite? ›

Well, the alphabet \Sigma is finite, and therefore regular, and the star operation preserves regularity (by the definition of regular languages).

Do all DFAS accept the empty string? ›

Yes. This is immediate from the definitions. A DFA accepts if it's in an accepting state after it's read its input. If the input is the empty string, the DFA makes no transitions so, after reading it's input, it's still in its initial state, q0.

Why is empty string false? ›

In JavaScript, an empty string is also known as a falsy. A “falsy” is any value that, in a boolean, would equate to false. A null, an undefined, and an empty string are all examples of falsies. The opposite of a falsy is, you guessed it, a truthy.

Is empty string the same as \0? ›

The difference is that if the string is empty then string_variable[0] has undefined behavior; There is no index 0 unless the string is const -qualified. If the string is const qualified then it will return a null character.

What is the hex value for empty string? ›

NULL terminator (or 0x00) in a string - hex.

What is ∈ or ∉? ›

meaning "A contains or includes x". The negation of set membership is denoted by the symbol "∉". Writing. means that "x is not an element of A". The symbol ∈ was first used by Giuseppe Peano, in his 1889 work Arithmetices principia, nova methodo exposita.

What is called in this ∃ symbol? ›

∃ (the existential quantifier) means “there exists” and was first used in the 1897 book For- mulaire de mathematiqus by Giuseppe Peano (1858-1932).

What is the backwards 3 Greek letter? ›

One, the most common in modern typography and inherited from medieval minuscule, looks like a reversed number "3" and is encoded U+03B5 ε GREEK SMALL LETTER EPSILON.

What is null in coding? ›

Computing. Null (SQL) (or NULL), a special marker and keyword in SQL indicating that something has no value. Null character, the zero-valued ASCII character, also designated by NUL, often used as a terminator, separator or filler. This symbol has no visual representation.

Can we pass string as null? ›

It is a special value that we can assign to any reference type variable. We can cast null into any type in which we want, such as string, int, double, etc.

Is null character a string? ›

The null character indicates the end of the string. Such strings are called null-terminated strings. The null terminator of a multibyte string consists of one byte whose value is 0.

What is empty vs blank string? ›

We consider a string to be empty if it's either null or a string without any length. If a string only consists of whitespace, then we call it blank.

What does string Isblank mean? ›

isBlank() is an instance method that returns true if the string is empty or contains only white space codepoints. This method was introduced in Java 11. If the string contains only white spaces, then applying this method will return true .

What is opposite to Isblank? ›

The Excel ISBLANK function returns TRUE when a cell contains is empty, and FALSE when a cell is not empty. For example, if A1 contains "apple", ISBLANK(A1) returns FALSE. The Excel NOT function returns the opposite of a given logical or boolean value.

What is an example of a NULL value? ›

A null value indicates a lack of a value, which is not the same thing as a value of zero. For example, consider the question "How many books does Adam own?" The answer may be "zero" (we know that he owns none) or "null" (we do not know how many he owns).

How do you handle null strings? ›

10 Tips to Handle Null Effectively
  1. Don't Overcomplicate Things. ...
  2. Use Objects Methods as Stream Predicates. ...
  3. Never Pass Null as an Argument. ...
  4. Validate Public API Arguments. ...
  5. Leverage Optional. ...
  6. Return Empty Collections Instead of Null. ...
  7. Optional Ain't for Fields. ...
  8. Use Exceptions Over Nulls.
Jan 26, 2017

What is the full meaning of null? ›

1. : having no legal or binding force : invalid. a null contract. 2. : amounting to nothing : nil.

Does null mean yes or no? ›

NULL is used to represent "no value" and allow that to be distinguished between 1 and 0, true or false, or an empty string versus a string with content.

Why do people use null? ›

The basic rule is simple: null should only be allowed when it makes sense for an object reference to have 'no value associated with it'. (Note: an object reference can be a variable, constant, property (class field), input/output argument, and so on.) Every person has a name.

Does null mean blank or zero? ›

Answer: Null indicates there is no value within a database field for a given record. It does not mean zero because zero is a value. Blank indicates there is a value within a database but the field is blank.

Is An empty string the same as null? ›

The Java programming language distinguishes between null and empty strings. An empty string is a string instance of zero length, whereas a null string has no value at all. An empty string is represented as "" . It is a character sequence of zero characters.

Does empty string take more space than null? ›

In innoDB, NULL occupies less space as compared to empty string. Also, the NULL length is null while length of the empty string is 0. From the above output it is clear that the length of the empty string is 1. The above output means that count is 0 for null value.

Should we use string empty? ›

Behind the scenes String. Empty works exactly same as "" . Both will give you pointer to the same interned value. It is just a style matter of your choosing and not a performance-based decision.

What is the difference between blank and null? ›

The fundamental difference between these two is that null controls the validation at the database level, and blank is used during form field validation at the application level.

Is An empty string null or undefined? ›

In JavaScript, “” represents the empty string, and we can use the null keyword to initialize the string with a null value. If we don't assign any value to any variable, it is undefined by default.

How do you replace null with empty string in SQL? ›

There are two ways to replace NULL with blank values in SQL Server, function ISNULL(), and COALESCE(). Both functions replace the value you provide when the argument is NULL like ISNULL(column, '') will return empty String if the column value is NULL.

How do I check if a string is empty? ›

Java String isEmpty() Method

The isEmpty() method checks whether a string is empty or not. This method returns true if the string is empty (length() is 0), and false if not.

Does an empty string equal false? ›

Empty strings are "falsy" which means they are considered false in a Boolean context, so you can just use not string.

Is empty string same as whitespace? ›

First you should know the difference between empty string and a white space. The length of a white ' ' space is 1 . An empty string '' will have a length zero.

How much memory does an empty string take? ›

For an empty string, length is 0.

Why is string empty better? ›

Empty is also generally going to be easier and maybe more accurate than looking for the literal. It also clarifies intent: you didn't just make a typo or forget to finish something, you really did want empty string. The performance reason is due to interning.

What does empty string evaluate to? ›

An empty string is evaluated to be false .

Does null mean nothing? ›

Null also means invalid, or having no binding force. From the Latin nullus, meaning "not any," poor, powerless null is not actually there at all. Or if it was, it's gone now. Because null is basically nothing, zip, zilch, nada, and nix.


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