Whitelist permitted types when adding constraint in integer_underflow.py

mythril/analysis/modules/integer_underflow.py

@@ -52,6 +52,9 @@ def execute(statespace):
 
                 logging.debug("[INTEGER_UNDERFLOW] Checking SUB " + str(op0) + ", " + str(op1) + " at address " + str(instruction['address']))
 
+                allowed_types = [int, BitVecRef, BitVecNumRef]
+
+                if type(op0) in allowed_types and type(op1) in allowed_types:
                     constraints.append(UGT(op1,op0))
 
                     try: