[BugFix] Better make_composite_from_td

ghstack-source-id: c99dfa6
Pull-Request-resolved: #2952

Author: Vincent Moens

torchrl/envs/utils.py

@@ -938,7 +938,7 @@ def make_composite_from_td(
     # of unbounded values.
     def make_shape(shape):
         if shape or not unsqueeze_null_shapes:
-            if dynamic_shape:
+            if dynamic_shape and shape:
                 return shape[:-1] + (-1,)
             else:
                 return shape
@@ -954,7 +954,8 @@ def make_shape(shape):
             if is_tensor_collection(tensor) and not is_non_tensor(tensor)
             else NonTensor(
                 shape=tensor.shape,
-                example_data=tensor.data,
+                # Assume all the non-tensors have the same datatype
+                example_data=tensor.view(-1)[0].data,
                 device=tensor.device,
             )
             if is_non_tensor(tensor)