Add missing canRequireSQLConversion() in example type code

en/cookbook/advanced-field-value-conversion-using-custom-mapping-types.rst

@@ -171,6 +171,11 @@ Now we're going to create the ``point`` type and implement all required methods.
             return $value;
         }
 
+        public function canRequireSQLConversion()
+        {
+            return true;
+        }
+
         public function convertToPHPValueSQL($sqlExpr, AbstractPlatform $platform)
         {
             return sprintf('AsText(%s)', $sqlExpr);