Fix using OpenAiInferenceEngine for LLMAsJudge (#1194)

Signed-off-by: Yifan Mai <yifan@cs.stanford.edu>
Co-authored-by: Elron Bandel <elronbandel@gmail.com>

src/unitxt/llm_as_judge.py

@@ -144,13 +144,13 @@ def verify(self):
             )
 
         if isinstance(self.inference_model, OpenAiInferenceEngine):
-            if self.format:
+            if self.format and type(self.format) is not SystemFormat:
                 raise ValueError(
                     "Error in 'LLMAsJudge' metric. Inference model 'OpenAiInferenceEngine' does "
                     "not support formatting. Please remove the format definition from the recipe"
                     " (OpenAi Chat API take care of the formatting automatically)."
                 )
-            if self.system_prompt:
+            if self.system_prompt and type(self.system_prompt) is not EmptySystemPrompt:
                 raise ValueError(
                     "Error in 'LLMAsJudge' metric. Inference model 'OpenAiInferenceEngine' does "
                     "not support system prompt. Please remove the system_prompt definition from the recipe"