FIELD_INTEGRITY_EXCEPTION: Failed to save undefined: QualifiedName is required for descriptors: Source
Save error: A problem was encountered while invoking the subscription method
If in the Salesforce 'Developer Console' you get the error mentioned in the subject or if you in Eclipse Force.com IDE you get:
Save error: A problem was encountered while invoking the subscription method: No TOKENS named markup://c:defaultTokens foundproblem Save error: COMPONENT's markup cannot be empty. If you are trying to delete the Lightning definition bundle, directly delete the bundle instead. Save error: QualifiedName is required for descriptors
Then ensure that you don't have an empty `controller=""` attribute, this took a me a little while to notice so for the prosperity of others and my own memory forming benefit I am posting this. If this has helped you feel free to follow @danielsokolows or thanks comment.