ZeroDivisionError in context_relevance (#154)

Changed: python3.9/site-packages/ragas/metrics/context_relevance.py",
line 162, in _score_batch

From: `score = min(len(indices) / len(context_sents), 1)`

To: ``` if len(context_sents) == 0:
                        score = 0
                else:
score = min(len(indices) / len(context_sents), 1)```

fixes: #153

Co-authored-by: devtribble <[email protected]>

src/ragas/metrics/context_relevance.py

@@ -159,7 +159,10 @@ def _score_batch(
                         if output.lower() != "insufficient information."
                         else []
                     )
-                    score = min(len(indices) / len(context_sents), 1)
+                    if len(context_sents) == 0:
+                        score = 0
+                    else:
+                        score = min(len(indices) / len(context_sents), 1)
                     overlap_scores.append(score)
                 if self.strictness > 1:
                     agr_score = self.sent_agreement.evaluate(n_response)