message: Allow groups=None
diff: @@ -138,7 +138,7 @@ class Conv(Layer):
  if filters is not None and not isinstance(filters, int):
  filters = int(filters)
  self.filters = filters
  - self.groups = groups
  + self.groups = groups or 1
  if filters is not None and filters % self.groups != 0:
  raise ValueError(
  'The number of filters must be evenly divisible by the number of '
  