Use only string value in error message

Signed-off-by: Lisa Velden <velden@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>

diff --git a/src/Ganeti/WConfd/ConfigModifications.hs b/src/Ganeti/WConfd/ConfigModifications.hs
index 9e66609..aead178 100644 (file)
--- a/src/Ganeti/WConfd/ConfigModifications.hs
+++ b/src/Ganeti/WConfd/ConfigModifications.hs
@@ -303,7 +303,7 @@ attachInstanceDiskChecks uuidInst uuidDisk idx' cs = do
   let insts = M.elems . fromContainer . configInstances . csConfigData $ cs
   forM_ insts (\inst' -> when (uuidDisk `elem` instDisks inst') . Bad
     . ReservationError $ printf "Disk %s already attached to instance %s"
-        uuidDisk (show $ instName inst))
+        uuidDisk (show . fromMaybe "" $ instName inst))
 
 -- * Pure config modifications functions