The Type NULL has only one possible value which is the value NULL.To give a variable the NULL value you should simply assign it such as follows:

the NUL type is capitalized by convention, but in fact it is incasesensitive. you can give the NULL type in lowercase letter too
such as follows:

so what doess NULL really mean?
actually the term “NULL” is nothing.NULL does not mean zero or blank space.It means no value or nothing.
ther is a diffrence between a variable that has not yet been assigned and a variable that has a null value

The ways that a NULL value would be created

• It has been specifically assigned the value Null.
• It has been erased using the function unset().
• It has not been set to any predefined value.

Related posts:

1. Assigning Variables in PHP
2. PHP Variables Basic
3. Integer Type in PHP
4. Boolean Types in PHP
5. Variable Types in PHP
6. Double Type in PHP