I had a source file with an unresolved identifier and the Import Management
Tool showed me the identifier in the first step.

I typed in a package name and hit enter.  I then tried to remove the
package name by selecting it, deleting the text and hitting enter.
This generated two popups:

    Information
    Invalid value. The property Package Name could not be set.  Reason:
    Name TreeMap mismatch

    Exception
    Invalid value.  The property Package Name could not be set.  Reason:
    null

I could not get the Exception dialog to show the details.

A second attempt to delete the name succeeded.