Support using null-safe operator with null value (#55175)

* Add test

* Mark `<=>` operator as valid for `null` comparisons

Author: willrowe

src/Illuminate/Database/Query/Builder.php

@@ -866,7 +866,7 @@ public function where($column, $operator = null, $value = null, $boolean = 'and'
         // where null clause to the query. So, we will allow a short-cut here to
         // that method for convenience so the developer doesn't have to check.
         if (is_null($value)) {
-            return $this->whereNull($column, $boolean, $operator !== '=');
+            return $this->whereNull($column, $boolean, ! in_array($operator, ['=', '<=>'], true));
         }
 
         $type = 'Basic';
@@ -958,7 +958,7 @@ public function prepareValueAndOperator($value, $operator, $useDefault = false)
     protected function invalidOperatorAndValue($operator, $value)
     {
         return is_null($value) && in_array($operator, $this->operators) &&
-             ! in_array($operator, ['=', '<>', '!=']);
+             ! in_array($operator, ['=', '<=>', '<>', '!=']);
     }
 
     /**

tests/Database/DatabaseQueryBuilderTest.php

@@ -5030,6 +5030,10 @@ public function testProvidingNullWithOperatorsBuildsCorrectly()
         $builder = $this->getBuilder();
         $builder->select('*')->from('users')->where('foo', '<>', null);
         $this->assertSame('select * from "users" where "foo" is not null', $builder->toSql());
+
+        $builder = $this->getBuilder();
+        $builder->select('*')->from('users')->where('foo', '<=>', null);
+        $this->assertSame('select * from "users" where "foo" is null', $builder->toSql());
     }
 
     public function testDynamicWhere()