make fix-copies

Author: patrickvonplaten

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_diffedit.py

@@ -560,7 +560,7 @@ def _encode_prompt(
             uncond_tokens: List[str]
             if negative_prompt is None:
                 uncond_tokens = [""] * batch_size
-            elif type(prompt) is not type(negative_prompt):
+            elif prompt is not None and type(prompt) is not type(negative_prompt):
                 raise TypeError(
                     f"`negative_prompt` should be the same type to `prompt`, but got {type(negative_prompt)} !="
                     f" {type(prompt)}."