implement isNumericType

src/main/java/de/hsrm/compiler/Klang/types/NullType.java

@@ -33,4 +33,9 @@ public class NullType extends Type {
         return false;
     }
 
+    @Override
+    public boolean isNumericType() {
+        return false;
+    }
+
 }

src/main/java/de/hsrm/compiler/Klang/types/StructType.java

@@ -46,4 +46,9 @@ public class StructType extends Type {
 
         return false;
     }
+
+    @Override
+    public boolean isNumericType() {
+        return false;
+    }
 }