fix issue 260 for the CP-SAT solver

examples/tests/issue260.py

@@ -0,0 +1,10 @@
+#from ortools.constraint_solver import pywrapcp
+from ortools.sat.python import cp_model
+
+model = cp_model.CpModel()
+y = model.NewIntVar(0, 3, 'y')
+y == None
+
+#solver = pywrapcp.Solver('my solver')
+#x = solver.IntVar(0, 3, 'var_name')
+#x == None

ortools/sat/python/cp_model.py

@@ -218,6 +218,8 @@ class IntegerExpression(object):
     return _ProductCst(self, -1)
 
   def __eq__(self, arg):
+    if arg is None:
+      return False
     if isinstance(arg, numbers.Integral):
       AssertIsInt64(arg)
       return BoundIntegerExpression(self, [arg, arg])
@@ -257,6 +259,8 @@ class IntegerExpression(object):
       return BoundIntegerExpression(self - arg, [1, INT_MAX])
 
   def __ne__(self, arg):
+    if arg is None:
+      return True
     if isinstance(arg, numbers.Integral):
       AssertIsInt64(arg)
       if arg == INT_MAX: