In the definition of DataLoader, the argument batch_size defaults to 1, even when sampler is also specified. This causes it to appear that the batch_size is 1 even if sampler is doing something more complex. This makes it difficult to determine if DataLoader's batch_size attribute is correct or if we should prove sampler for more details because sampler is always specified.

What should happen is batch_size should default to None, and if no sampler is specified, then it should change its value to 1. This change will make it simple to see that the batch_size attribute of DataLoader` might not be used.