Fixing issue where 0 is discarded as a valid timestamp (#46158)

Author: rojtjo

src/Illuminate/Validation/Concerns/ValidatesAttributes.php

@@ -249,7 +249,7 @@ protected function compareDates($attribute, $value, $parameters, $operator)
             return $this->checkDateTimeOrder($format, $value, $parameters[0], $operator);
         }
 
-        if (! $date = $this->getDateTimestamp($parameters[0])) {
+        if (is_null($date = $this->getDateTimestamp($parameters[0]))) {
             $date = $this->getDateTimestamp($this->getValue($parameters[0]));
         }
 

tests/Validation/ValidationValidatorTest.php

@@ -5028,6 +5028,12 @@ public function testBeforeAndAfter()
 
         $v = new Validator($trans, ['x' => '17:44'], ['x' => 'After:17:44:00']);
         $this->assertTrue($v->fails());
+
+        $v = new Validator($trans, ['x' => '0001-01-01T00:00'], ['x' => 'before:1970-01-01']);
+        $this->assertTrue($v->passes());
+
+        $v = new Validator($trans, ['x' => '0001-01-01T00:00'], ['x' => 'after:1970-01-01']);
+        $this->assertTrue($v->fails());
     }
 
     public function testBeforeAndAfterWithFormat()