Update glu check (#1689)

* update glu check

* separate out type check

* fix test

* update docs

* type ignore

Author: mvpatel2000

composer/algorithms/gated_linear_units/gated_linear_units.py

@@ -100,17 +100,18 @@ def apply_gated_linear_units(model: torch.nn.Module,
 
         # get the activation functions used
         act_fns = {module.intermediate_act_fn for module in intermediate_modules}
-        if len(act_fns) == 0:
+        num_act_fns = len({type(act_fn) for act_fn in act_fns})
+        if num_act_fns == 0:
             raise ValueError('Tried to get the activation function from the model, but none were found. '
                              'Please specify `act_fn` manually to use Gated Linear Units.')
-        elif len(act_fns) > 1:
+        elif num_act_fns > 1:
             raise ValueError('Tried to get the activation function from the model, but multiple different '
                              'functions are used. This is currently unsupported with Gated Linear Units. '
                              'Please either use one activation function in BertIntermediate modules or '
                              'specify `act_fn` to manually override activation functions.')
 
-        # since our set is of 1, let's extract the only activation function remaining.
-        (act_fn,) = act_fns  #type: ignore will fail below if None
+        # since our set is of 1, let's extract the activation function
+        act_fn = next(iter(act_fns))  # type: ignore will fail below if None
 
         if act_fn is None:
             raise ValueError(