Impact analysis: better error report if the data model defines redundancy on a unidirectional relation (make it easier to troubleshoot for consultants)

SVN:trunk[4840]

core/relationgraph.class.inc.php

@@ -457,6 +457,10 @@ class RelationGraph extends SimpleGraph
 			{
 				// Get the upper neighbours
 				$sQuery = $aQueryInfo['sQueryUp'];
+				if (!$sQuery)
+				{
+					throw new Exception("Redundancy cannot be enabled on the relation $sRelCode/{$aQueryInfo['sDefinedInClass']}/{$aQueryInfo['sNeighbour']}: its direction is \"{$aQueryInfo['sDirection']}\"");
+				}
 				try
 				{
 					$oFlt = static::MakeSearch($sQuery);