Deciphering EclipseLink Error Messages

Suppose you get this:

Descriptor Exceptions: 
---------------------------------------------------------
Exception [EclipseLink-108] (Eclipse Persistence Services - 2.6.2.v20151217-774c696): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: Cannot find value in class indicator mapping in parent descriptor [null].
Descriptor: RelationalDescriptor(com.foobar.Foobar --> [DatabaseTable(FOOBAR)])
Exception [EclipseLink-41] (Eclipse Persistence Services - 2.6.2.v20151217-774c696): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A non-read-only mapping must be defined for the sequence number field.
Descriptor: RelationalDescriptor(com.foobar.Foobar --> [DatabaseTable(FOOBAR)])

That means, believe it or not, only that you have an abstract entity without any concrete entity specializing it.  That’s all it means.  It doesn’t have anything to do with sequence numbers, or (otherwise) badly mapped entities, or
updatable="false"
snippets.