avoid NullpointerException if close() method is called twice. See Bugzilla: #32403 Submitted by:	Wolf Siberski Reviewed by:	Bernhard Messer
avoid NullpointerException if close() method is called twice. See Bugzilla: #32403
Submitted by:	Wolf Siberski
Reviewed by:	Bernhard Messer


git-svn-id: 4c5078813df38efa56971a28e09a55254294f104@150686 13f79535-47bb-0310-9956-ffa450edef68

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