diff --git a/phalcon/Db/Adapter/Pdo/Mysql.zep b/phalcon/Db/Adapter/Pdo/Mysql.zep
index 77c485cbea1..4a07dd5d4e7 100644
--- a/phalcon/Db/Adapter/Pdo/Mysql.zep
+++ b/phalcon/Db/Adapter/Pdo/Mysql.zep
@@ -539,7 +539,7 @@ class Mysql extends PdoAdapter
             } elseif index["Non_unique"] == 0 {
                 let indexes[keyName]["type"] = "UNIQUE";
             } else {
-                let indexes[keyName]["type"] = null;
+                let indexes[keyName]["type"] = "";
             }
         }
 
diff --git a/phalcon/Db/Reference.zep b/phalcon/Db/Reference.zep
index cae50456a51..eaeb72d0001 100644
--- a/phalcon/Db/Reference.zep
+++ b/phalcon/Db/Reference.zep
@@ -59,7 +59,7 @@ class Reference implements ReferenceInterface
      *
      * @var string
      */
-    protected referencedSchema { get };
+    protected referencedSchema = "" { get };
 
     /**
      * Referenced Table
@@ -73,21 +73,21 @@ class Reference implements ReferenceInterface
      *
      * @var string
      */
-    protected schemaName { get };
+    protected schemaName = "" { get };
 
     /**
      * ON DELETE
      *
      * @var string
      */
-    protected onDelete { get };
+    protected onDelete = "" { get };
 
     /**
      * ON UPDATE
      *
      * @var string
      */
-    protected onUpdate { get };
+    protected onUpdate = "" { get };
 
     /**
      * Phalcon\Db\Reference constructor