Issue #702: Fix Location on Map field undefined error.

tripal_chado/includes/TripalFields/ogi__location_on_map/ogi__location_on_map.inc

@@ -322,10 +322,11 @@ class ogi__location_on_map extends ChadoField {
       }
     }
 
+
     // If there are no map positions expanded above then remove the stub.
     // This is needed to ensure this field isn't displayed when there are no locations.
     if (!isset($feature->featurepos->feature_id) OR (sizeof($feature->featurepos->feature_id) == 0)) {
-      unset($entity->{$field_name});
+      $entity->{$field_name}['und'][0]['value'] = array();
     }
   }