[interchange] Suppress error message in [assign] when using the documented behaviour of passing an empty string.

commit 5479b9aa307d8eb6f3d158949beca730c582879a
Author: Stefan Hornburg (Racke) <[email protected]>
Date:   Sat Dec 15 13:45:34 2012 +0100

    Suppress error message in [assign] when using the documented behaviour of passing an empty string.

 code/SystemTag/assign.coretag |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)
---
diff --git a/code/SystemTag/assign.coretag b/code/SystemTag/assign.coretag
index c582902..8e2cdfb 100644
--- a/code/SystemTag/assign.coretag
+++ b/code/SystemTag/assign.coretag
@@ -34,11 +34,13 @@ sub {
 			$Vend::Session->{assigned}{$_} = $value;
 		}
 		else {
-			logError(
-				"Attempted assign of non-numeric '%s' to %s. Deleted.",
-				$value,
-				$_,
-			);
+            if ($value) {
+    			logError(
+	    			"Attempted assign of non-numeric '%s' to %s. Deleted.",
+		    		$value,
+			    	$_,
+			    );
+            }
 			delete $Vend::Session->{assigned}{$_};
 		}
 	}