fix: handle empty string in ChatSession.send_message (#134)

* fix: handle empty string in ChatSession.send_message

* refactor: move empty string handling to content_types.to_content

* ValueError

---------

Co-authored-by: Mark Daoust <[email protected]>

Author: Hamza-nabil

google/generativeai/types/content_types.py

@@ -190,6 +190,9 @@ def is_content_dict(d):
 
 
 def to_content(content: ContentType):
+    if not content:
+        raise ValueError("content must not be empty")
+
     if isinstance(content, Mapping):
         content = _convert_dict(content)