#136
When the URL is found to be null and classLoaders is not null, assuming an extension is at cause, null the classLoaders and try again.  This should result in trying the DataCleaner default provided images.  If the classLoaders were specific to DataCleaner, then this will cause one more attempt.  However, I expect this to be a rare case.
#136
Fixed "input = null" dialog message.  This was due to missing return statement when trying to check the default class for images.
Merge pull request #137 from mhorner7wd/master

#136 Fixed exception when image not found in imported extension