Fix bad merge into master

This should only have been reverted in 7.0, but not for 7.1. (merge=ours??)
Added appropriate NEWS entry.

NEWS

@@ -9,6 +9,7 @@ PHP                                                                        NEWS
   . Fixed bug #62814 (It is possible to stiffen child class members visibility).
     (Nikita)
   . Fixed bug #69989 (Generators don't participate in cycle GC). (Nikita)
+  . Fixed bug #71428 (Inheritance and allow_null). (Joe)
   . Fixed bug #71572 (String offset assignment from an empty string inserts
     null byte). (Francois)
   . Implemented the RFC `Support Class Constant Visibility`. (Sean DuBois,

Zend/tests/bug71428.1.phpt

@@ -1,7 +1,5 @@
 --TEST--
 bug #71428.1: inheritance with null default values
---XFAIL--
-This is a BC break
 --FILE--
 <?php
 class A {

Zend/tests/bug71428.3.phpt

@@ -1,7 +1,5 @@
 --TEST--
 bug #71428: Validation type inheritance with = NULL
---XFAIL--
-This is a BC break
 --FILE--
 <?php
 class A { }

Zend/tests/bug72119.phpt

@@ -14,5 +14,5 @@ class Hello implements Foo {
 }
 echo "OK\n";
 ?>
---EXPECT--
-OK
+--EXPECTF--
+Fatal error: Declaration of Hello::bar(array $baz = Array) must be compatible with Foo::bar(array $baz = NULL) in %s on line %d

Zend/zend_inheritance.c

@@ -319,13 +319,10 @@ static zend_bool zend_do_perform_implementation_check(const zend_function *fe, c
 			return 0;
 		}
 
-#if 0
-		// This introduces BC break described at https://bugs.php.net/bug.php?id=72119
 		if (proto_arg_info->type_hint && proto_arg_info->allow_null && !fe_arg_info->allow_null) {
 			/* incompatible nullability */
 			return 0;
 		}
-#endif
 
 		/* by-ref constraints on arguments are invariant */
 		if (fe_arg_info->pass_by_reference != proto_arg_info->pass_by_reference) {