PHP NULL type:

In PHP 4 a special type of value is introduced, which indicates that a variable does not consists of any value or NULL value. NULL is the only value of NULL datatype.

A variable is considered to be NULL if we use unset() method on a variable, or a NULL value is assigned to the variable, no value is yet assigned to it.

Two special functions are used in this context, is_null() and unset(). is_null() function is used to check whether a  variable is NULL assigned or it has some value.

PHP Null Type Example:

$a;

echo "1=True and Blank=False".is_null($a)."<br/>";

$a=23;

echo "1=True and Blank=False".is_null($a)."<br/>";

$a=NULL;

echo "1=True and Blank=False".is_null($a)."<br/>";

$a=12;

echo "1=True and Blank=False".is_null($a)."<br/>";

unset($a);

echo "1=True and Blank=False".is_null($a)."<br/>";

Output: 

1=True and Blank=False1
1=True and Blank=False
1=True and Blank=False1
1=True and Blank=False
1=True and Blank=False1

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