[TYPO3-rte] how to eliminate alt="undefined" in link icons?

[Stephan Bernhard]

hi list

there is anaother problem with this annoying error:

when working with feeditadvanced and inserting/updating a link in a 
content element the generated link shows "undefined" instead of 
inserting the accessibility icon.

doing the same in the BE everything is ok, the accessibility icon is set 
- besides that RTEhtmlarea inserts the attribute alt="undefined" in the 
img tag.

so, where is the crucial error?
in RTEhtmlarea or in feeditadvanced?

thanks for further hints and help.
stephan