PHP isset() vs empty() vs is_null()

Value of variable ($var)	isset($var)	empty($var)	is_null($var)
“” (an empty string)	bool(true)	bool(true)
” ” (space)	bool(true)
FALSE	bool(true)	bool(true)
TRUE	bool(true)
array() (an empty array)	bool(true)	bool(true)
NULL		bool(true)	bool(true)
“0” (0 as a string)	bool(true)	bool(true)
0 (0 as an integer)	bool(true)	bool(true)
0.0 (0 as a float)	bool(true)	bool(true)
var $var; (a variable declared, but without a value)		bool(true)	bool(true)
NULL byte (“\ 0”)	bool(true)