Backport r938141 by tmcguire from trunk to the 4.2 branch:

Merged revisions 934942 via svnmerge from 
svn+ssh://tmcguire@svn.kde.org/home/kde/branches/kdepim/enterprise4/kdepim

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  r934942 | tmcguire | 2009-03-04 10:27:01 +0100 (Wed, 04 Mar 2009) | 12 lines
  
  Merged revisions 931708 via svnmerge from 
  svn+ssh://tmcguire@svn.kde.org/home/kde/branches/kdepim/enterprise/kdepim
  
  ........
    r931708 | winterz | 2009-02-25 18:39:48 +0100 (Wed, 25 Feb 2009) | 5 lines
    
    in makeShowAuditLogLink, return empty QString if the auditLog is empty.
    fixes kolab/issue3436
    
    Should be merged into all branches.
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svn path=/branches/KDE/4.2/kdepim/; revision=938246

objecttreeparser.cpp

@@ -2099,12 +2099,16 @@ static QString makeShowAuditLogLink( const QString & auditLog ) {
   if ( auditLog.isEmpty() )
     return i18n("No Audit Log available");
 
-  KUrl url;
-  url.setProtocol( "kmail" );
-  url.setPath( "showAuditLog" );
-  url.addQueryItem( "log", auditLog );
+  if ( !auditLog.isEmpty() ) {
+    KUrl url;
+    url.setProtocol( "kmail" );
+    url.setPath( "showAuditLog" );
+    url.addQueryItem( "log", auditLog );
 
-  return "<a href=\"" + url.url() + "\">" + i18nc("The Audit Log is a detailed error log from the gnupg backend", "Show Audit Log") + "</a>";
+    return "<a href=\"" + url.url() + "\">" + i18nc("The Audit Log is a detailed error log from the gnupg backend", "Show Audit Log") + "</a>";
+  }
+
+  return QString();
 }
 
 static QString endVerboseSigstatHeader( const PartMetaData & pmd )