Metatype AD empty String default value

I have an AD with a default value which is an empty string, like

<AD id="server" type="String" default=""/>

According to the OSGi Spec, the method AttributeDefinition.defaultValue() in this case must return an array with one element (which should be the empty string), because the cardinality is 0 (implicit) and the default is defined.

However, the Felix Metatype Service implementation returns null for defaultValue().

In my use case, this breaks everything, because a null value indicates a configuration error (default not given, although mandatory) whereas an empty string is perfectly fine.