Simplifying ensureValidDocument() function

Author: petr-buchin

src/functions.php

@@ -7,7 +7,9 @@
 
 function ensureValidDocument($document) {
     if ($document instanceof Serializable) {
-        $document = $document->bsonSerialize();
+        // do not validate Serializable instances since call to Serializable::bsonSerialize()
+        // will increase a memory usage by creating array|object copy of the document
+        return;
     }
 
     $arrayDocument = (array) $document;
@@ -21,11 +23,6 @@ function ensureValidDocument($document) {
                 )
             );
         }
-
-        // Check nested document, if it's not a circular reference to the current $document
-        if ((is_array($value) || is_object($value)) && !$value === $document) {
-            ensureValidDocument($value);
-        }
     }
 }