Index: trunk/ippScripts/scripts/detrend_resid.pl
===================================================================
--- trunk/ippScripts/scripts/detrend_resid.pl	(revision 10544)
+++ trunk/ippScripts/scripts/detrend_resid.pl	(revision 10592)
@@ -97,5 +97,5 @@
 $outputRoot = $ipprc->convert_filename_absolute( $outputRoot );
 $input_uri = $ipprc->convert_filename_absolute( $input_uri );
-$detrend = $ipprc->convert_filename_absolute( $detrend );
+$detrend = $ipprc->convert_filename_absolute( $detrend ) if defined $detrend;
 
 my $outputName = $ipprc->filename("PPIMAGE.OUTPUT", $outputRoot, $class_id);