What is the difference between empty and is_null? _PHP Tutorial

What is the difference between empty and is_null?

bool empty ( mixed $var )

If var is a non-empty or non-zero value, empty() returns FALSE. In other words, "", 0, "0", NULL, FALSE, array(), var $var; and objects without any properties will be considered empty, and TRUE is returned if var is empty.

empty() is the antonym of (boolean) var except that it does not produce a warning when the variable is not set. See Converting to Boolean for more information.
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A variable is considered NULL in the following situations:

bool is_null ( mixed $var )

Returns TRUE if var is null, FALSE otherwise.

is assigned the value NULL.

has not been assigned a value yet.

is unset().