fix: preserve null equality conditions

Author: Bennett-hash

src/Parse/ParseQuery.php

@@ -160,7 +160,7 @@ public function equalTo($key, $value)
      */
     private function addCondition($key, $condition, $value)
     {
-        if (!isset($this->where[$key])) {
+        if (!array_key_exists($key, $this->where)) {
             $this->where[$key] = [];
         } elseif (!$this->isConditionMap($this->where[$key])) {
             $this->where[$key] = ['$eq' => $this->where[$key]];

tests/Parse/ParseQueryTest.php

@@ -2827,6 +2827,25 @@ public function testEqualToAfterDirectEqualityDoesNotOverrideOtherConditions()
         ], $query->_getOptions());
     }
 
+    /**
+     * @group query-equalTo-conditions
+     */
+    public function testEqualToNullBeforeConditionPreservesNullEquality()
+    {
+        $query = new ParseQuery('TestObject');
+        $query->equalTo('status', null);
+        $query->notEqualTo('status', 'archived');
+
+        $this->assertSame([
+            'where' => [
+                'status' => [
+                    '$eq' => null,
+                    '$ne' => 'archived',
+                ]
+            ],
+        ], $query->_getOptions());
+    }
+
     /**
      * @group query-equalTo-conditions
      */