throwing import error if nltk not available in detect_pii mock

Author: AlejandroEsquivel

tests/integration_tests/test_assets/validators/detect_pii.py

@@ -1,6 +1,5 @@
 from typing import Any, Callable, Dict, List, Union
 import difflib
-import nltk
 
 from guardrails.validator_base import (
     FailResult,
@@ -65,6 +64,14 @@ def chunking_function(self, chunk: str):
         Because using the tokenizer is expensive, we only use it if
         there is a period present in the chunk.
         """
+        try:
+            import nltk
+        except ImportError:
+            raise ImportError(
+                "nltk is required for sentence splitting. Please install it using "
+                "`poetry add nltk`"
+            )
+
         # using the sentence tokenizer is expensive
         # we check for a . to avoid wastefully calling the tokenizer
         if "." not in chunk: