made UncomputableOp support None as an argument

(needed to express that gradient with respect to x is undefined if x is allowed to be None)

made UncomputableOp support None as an argument
c171d871 · Ian Goodfellow · 2d299c61 · c171d871
--- a/theano/gof/op.py
+++ b/theano/gof/op.py
@@ -636,6 +636,8 @@ class UncomputableOp(Op):
        return "Uncomputable{%s,%s}"%(self.exc,self.msg)

    def make_node(self,x):
+        if x is None:
+            x = graph.Constant(theano.gof.type.generic,None)
        return graph.Apply(self, [x], [x.type()] )

    def perform(self, node, inputs, out_storage):