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The special NULL value represents that a variable has no value. NULL is the only possible value of type NULL.


The null type was introduced in PHP 4.

A variable is considered to be NULL if

  • it has been assigned the constant NULL.

  • it has not been set to any value yet.

  • it has been unset().


There is only one value of type NULL, and that is the case-insensitive keyword NULL.

= NULL;      

See also is_null() and unset().