Major Description
When an OSGi configuration property is removed from the dictionary associated to a component, the default value assigned to it is an empty string.
When such an empty string is processed by DocumentNodeStoreService#prop, it is returned to its caller as a valid configuration value. The callers of DocumentNodeStoreService#prop, instead, expect null when such an empty value is found.
The method DocumentNodeStoreService#prop should check for empty strings in the OSGi configuration, and treat them as null values.