diff --git a/AlgebraicDataflowArchitectureModel/src/models/algebra/Term.java b/AlgebraicDataflowArchitectureModel/src/models/algebra/Term.java
index 9cc7de2..2a22051 100644
--- a/AlgebraicDataflowArchitectureModel/src/models/algebra/Term.java
+++ b/AlgebraicDataflowArchitectureModel/src/models/algebra/Term.java
@@ -385,7 +385,7 @@
 			if (implParamOrder == null) {
 				String exp = null;
 				String receiver = "";
-				if (children.get(0) != null) {
+				if (children.size() > 0 && children.get(0) != null) {
 					receiver = children.get(0).toImplementation(sideEffects);
 					exp = receiver + "." + symbol.toImplementation() + "(";
 				} else {
diff --git a/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java b/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
index 18382a0..04685d9 100644
--- a/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
+++ b/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
@@ -955,7 +955,8 @@
 	public static final Symbol lookup = new Symbol("lookup", 2, Symbol.Type.PREFIX, "get", Symbol.Type.METHOD, new Symbol.ICalculator() {
 		@Override
 		public Expression calculate(List<Expression> args) {
-			if (args.get(1).getClass() == Constant.class && ((Constant) args.get(1)).getType().equals(typeString)) {
+			if (args.get(1).getClass() == Constant.class && 
+					((Constant) args.get(1)).getType() != null && ((Constant) args.get(1)).getType().equals(typeString)) {
 				String key = (String) ((Constant) args.get(1)).getValue();
 				if (args.get(0) instanceof Term) {
 					Term term = (Term) args.get(0);