fix use_mask_in_transformer=False

Author: hlky

src/diffusers/models/transformers/transformer_lumina2.py

@@ -129,7 +129,8 @@ def __call__(
 
         # scaled_dot_product_attention expects attention_mask shape to be
         # (batch, heads, source_length, target_length)
-        attention_mask = attention_mask.bool().view(batch_size, 1, 1, -1)
+        if attention_mask is not None:
+            attention_mask = attention_mask.bool().view(batch_size, 1, 1, -1)
 
         query = query.transpose(1, 2)
         key = key.transpose(1, 2)