distinct handle missing key in document

Author: jrattue

src/MockCollection.php

@@ -389,7 +389,7 @@ public function distinct($fieldName, $filter = [], array $options = [])
 
         $matcher = $this->matcherFromQuery($filter);
         foreach ($this->documents as $document){
-            if ($matcher($document)) {
+            if ($matcher($document) && isset($document[$fieldName])) {
                 $values[] = $document[$fieldName];
             }
         }

tests/MockCollectionTest.php

@@ -1175,6 +1175,7 @@ public function testDistinct()
         ]);
 
         self::assertThat($this->col->distinct('foo'), self::equalTo(['foo', 'bar', 'baz']));
+        self::assertThat($this->col->distinct('missing'), self::equalTo([]));
         self::assertThat($this->col->distinct('foo', ['bar' => 1]), self::equalTo(['foo', 'bar']));
         self::assertThat($this->col->distinct('foo', ['bar' => 2]), self::equalTo(['baz']));
     }