Warning: Undefined variable $a in %s on line %d

Warning: Trying to access array offset on value of type null in %s on line %d
NULL

Warning: Undefined variable $a in %s on line %d

Warning: Undefined variable $c in %s on line %d

Warning: Trying to access array offset on value of type null in %s on line %d
NULL

Warning: Undefined variable $a in %s on line %d
int(1)

Warning: Undefined variable $a in %s on line %d

Warning: Undefined variable $b in %s on line %d
int(0)

Warning: Undefined variable $a in %s on line %d
NULL

Warning: Undefined variable $b in %s on line %d
int(1)

Warning: Attempt to read property "1" on int in %s on line %d
NULL

Warning: Attempt to read property "1" on int in %s on line %d
NULL

Warning: Undefined variable $c in %s on line %d

Warning: Trying to access array offset on value of type null in %s on line %d

Warning: Attempt to read property "1" on int in %s on line %d

Warning: Attempt to read property "" on null in %s on line %d
NULL