use is_boolexpr

cpmpy/transformations/flatten_model.py

@@ -308,7 +308,7 @@ def get_or_make_var(expr,boolean=False):
         Determines whether this is a Boolean or Integer variable and returns
         the equivalent of: (var, normalize(expr) == var)
     """
-    if expr.is_bool():
+    if is_boolexpr(expr):
         boolean = True
     if __is_flat_var(expr) and boolean == expr.is_bool():
         return (expr, [])