Null & Nothingness

null does mean something!

What is nothingness? Is there nothingness only in outer space? If a tree falls in the forest and nobody listens, does it make a sound? Starting to see the point? Does nothing really mean nothing? To be or not to be? OK, I think we are going on a philosophical tangent, so let's get back to our geekiness:

null is Java's way to refer to "nothingness.", something that does not exist and has no value.

Full-Null Support

Full null support is the default in BoxLang, meaning you can use the null keyword and get real null values from databases or external services. Note that null is a reserved word so can't be used for variable names.

Note that if you are using the compat module then full null support is disabled unless you change the module settings for compat to enable it. You can do this programmatically via the Application.bx file, which can be used when building web applications. You can learn more about it here. In reality, you still could simulate null without full null support, and sometimes you get an empty string, sometimes a full Java null. So basically, the nonfull null support is a partial null support, which makes it hard for developers. So as a rule of thumb, we always recommend checking for nullness no matter WHAT!

Application.bx

class{
    this.nullSupport = true;
}

Checking For Nullness

Use the isNull() or isDefined() methods to evaluate for nothingness.

r = getMaybeData()
if( isNull( r ) ){
  // do something because r doesn't exist
}

if( isDefined( "r" ) ){

}

Also, remember that you can use the Elvis operator to test for null and an operator and expression.

results = getMaybeData() ?: "default value"

We would recommend that you use isNull() as it expresses coherently its purpose. Since isDefined() can also evaluate expressions.

Creating Nulls

You can create nulls in different ways in BoxLang. Let's explore these:

Approach	Full Null	Description
null keyword		r = null
Non returning function call		If a function returns nothing, its assignment will produce a null. function getNull(){} r = getNull()
nullValue()		r = nullValue()
javaCast( "null", "" )		r = javaCast( "null", "" )

In Practice

If you have three eggs and eat three eggs, then you might think you have "nothing," but in terms of eggs, you have "0". Zero is something, it’s a number, and it’s not nothing.

If you’re working with words and have a string like "hello" then delete the "h", "e", "l"s, and "o" you might think you’d end up with nothing, but you have "" which is an empty string. It’s still something.

Null in BoxLang is usually encountered when you ask for something that doesn’t exist. When looking at arrays, for instance, we created a list with five elements then asked BoxLang to give us the sixth element of that list. There is no sixth element, so BoxLang gave us null. It isn’t that there’s a blank in that sixth spot (""), it’s not a number 0, it’s nothingness – null.

Examples

function getData( filter ){

    if( isNull( arguments.filter ) ){
      // then do this
    } else {
      // use the filter
    }

}

function returnsNull(){
  if( key.exists( "invalid" ) ){
    return key[ "invalid" ];
  }
}

results = returnsNull();

writeOutput( isNull( results ) );

Also note that if a function returns nothing, it will be the same as returning null.