diff --git a/AlgebraicDataflowArchitectureModel/src/models/dataFlowModel/DataTransferChannel.java b/AlgebraicDataflowArchitectureModel/src/models/dataFlowModel/DataTransferChannel.java
index d6a81d9..dc09114 100644
--- a/AlgebraicDataflowArchitectureModel/src/models/dataFlowModel/DataTransferChannel.java
+++ b/AlgebraicDataflowArchitectureModel/src/models/dataFlowModel/DataTransferChannel.java
@@ -555,8 +555,10 @@
 			Expression pathValue = dstParams.get(i).getValue();
 			if (pathParam instanceof Variable) {
 				if (pathValue == null) {
-					dstParams.set(i, new AbstractMap.SimpleEntry<>(bindings.get((Variable) pathParam).getValue(), null));	// Replace a path parameter with a value in the unified message.
-					dependingVarPosInMessage.add(bindings.get((Variable) pathParam).getKey());		// The position of the replaced variable in the message.
+					if (bindings.get((Variable) pathParam) != null) {
+						dstParams.set(i, new AbstractMap.SimpleEntry<>(bindings.get((Variable) pathParam).getValue(), null));	// Replace a path parameter with a value in the unified message.
+						dependingVarPosInMessage.add(bindings.get((Variable) pathParam).getKey());		// The position of the replaced variable in the message.
+					}
 				} else {
 					// If the path parameter has a constraint.
 					if (pathValue instanceof Term) {