diff --git a/StandardPlugin/Extensions.cs b/StandardPlugin/Extensions.cs
index c8b3c72..3d96f1d 100644
--- a/StandardPlugin/Extensions.cs
+++ b/StandardPlugin/Extensions.cs
@@ -64,9 +64,14 @@ public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> items, in
 
         public static bool CanConvert(string srcUnitCode, string targetUnitCode)
         {
-            var targetUOM = RepresentationUnitSystem.UnitSystemManager.GetUnitOfMeasure(targetUnitCode);
-            var sourceUOM = RepresentationUnitSystem.UnitSystemManager.GetUnitOfMeasure(srcUnitCode);
-            return sourceUOM.Dimension == targetUOM.Dimension;
+            if (RepresentationUnitSystem.InternalUnitSystemManager.Instance.UnitOfMeasures[targetUnitCode] != null &&
+                RepresentationUnitSystem.InternalUnitSystemManager.Instance.UnitOfMeasures[srcUnitCode] != null)
+            {
+                var targetUOM = RepresentationUnitSystem.UnitSystemManager.GetUnitOfMeasure(targetUnitCode);
+                var sourceUOM = RepresentationUnitSystem.UnitSystemManager.GetUnitOfMeasure(srcUnitCode);
+                return sourceUOM.Dimension == targetUOM.Dimension;
+            }
+            return false;
         }
 
         public static bool CanConvertInto(this UnitOfMeasure srcUOM, string targetUnitCode)