unrelated bug in memory where we weren't throwing an error on empty s…

…tring for old_content

memgpt/memory.py

@@ -83,6 +83,9 @@ def edit_append(self, field, content, sep="\n"):
             raise KeyError(f'No memory section named {field} (must be either "persona" or "human")')
 
     def edit_replace(self, field, old_content, new_content):
+        if len(old_content) == 0:
+            raise ValueError("old_content cannot be an empty string (must specify old_content to replace)")
+
         if field == "persona":
             if old_content in self.persona:
                 new_persona = self.persona.replace(old_content, new_content)