Following is the output that you will see on PHP 7.1.7
Value of variable ($var)isset($var)empty($var)is_null($var)
"" (an empty string)bool(true) bool(true) bool(false)
" " (space)bool(true) bool(false) bool(false)
FALSEbool(true) bool(true) bool(false)
TRUEbool(true) bool(false) bool(false)
array() (an empty array)bool(true) bool(true) bool(false)
NULLbool(false) bool(true) bool(true)
"0" (0 as a string)bool(true) bool(true) bool(false)
0 (0 as an integer)bool(true) bool(true) bool(false)
0.0 (0 as a float)bool(true) bool(true) bool(false)
var $var; (a variable declared, but without a value)bool(false) bool(true) bool(true)
NULL byte ("\ 0")bool(true) bool(false) bool(false)