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--- a/src/internfile/mh_unknown.h
+++ b/src/internfile/mh_unknown.h
@@ -45,9 +45,7 @@
 	m_metaData["mimetype"] = "text/plain";
 	return true;
     }
-    virtual void clear() {
-	RecollFilter::clear(); 
-    }
+    virtual bool is_unknown() {return true;}
 };
 
 #endif /* _MH_UNKNOWN_H_INCLUDED_ */