avoid zero size batch caused by grad_accumulation

models/voicecraft.py

@@ -462,6 +462,8 @@ class VoiceCraft(nn.Module):
             before padding.
         """
         x, x_lens, y, y_lens = batch["x"], batch["x_lens"], batch["y"], batch["y_lens"]
+        if len(x) == 0:
+            return None
         x = x[:, :x_lens.max()] # this deal with gradient accumulation, where x_lens.max() might not be longer than the length of the current slice of x
         y = y[:, :, :y_lens.max()]
         assert x.ndim == 2, x.shape