Calling a non static method as static not allowed.

src/Faker/Provider/nl_NL/Person.php

@@ -288,15 +288,15 @@ public function title($gender = null)
      */
     public static function titleMale()
     {
-        return static::title();
+        return static::randomElement(static::$title);
     }
 
     /**
      * replaced by specific unisex dutch title
      */
     public static function titleFemale()
     {
-        return static::title();
+        return static::randomElement(static::$title);
     }
 
     /**