Preserve input empty strings

Author: steven10a

src/guardrails/agents.py

@@ -380,7 +380,8 @@ def _extract_text_from_input(input_data: Any) -> str:
                                     if field in part:
                                         text = part[field]
                                         break
-                                if text and isinstance(text, str):
+                                # Preserve empty strings, only filter None
+                                if text is not None and isinstance(text, str):
                                     text_parts.append(text)
                         if text_parts:
                             return " ".join(text_parts)
@@ -478,8 +479,8 @@ async def single_guardrail(ctx: RunContextWrapper[None], agent: Agent, input_dat
 
             except Exception as e:
                 if raise_guardrail_errors:
-                    # Re-raise the exception to stop execution
-                    raise e
+                    # Re-raise the exception to stop execution (preserve traceback)
+                    raise
                 else:
                     # Current behavior: treat errors as tripwires
                     # Return structured error info for consistency

tests/unit/test_agents.py

@@ -868,6 +868,24 @@ def test_extract_text_from_input_with_no_user_messages() -> None:
     assert result == ""  # noqa: S101
 
 
+def test_extract_text_from_input_preserves_empty_strings() -> None:
+    """Empty strings in content parts should be preserved, not filtered out."""
+    input_data = [
+        {
+            "role": "user",
+            "type": "message",
+            "content": [
+                {"type": "input_text", "text": "Hello"},
+                {"type": "input_text", "text": ""},  # Empty string should be preserved
+                {"type": "input_text", "text": "World"},
+            ],
+        }
+    ]
+    result = agents._extract_text_from_input(input_data)
+    # Empty string should be included, resulting in extra space
+    assert result == "Hello  World"  # noqa: S101
+
+
 # =============================================================================
 # Tests for updated agent-level guardrail behavior (stage_name and metadata)
 # =============================================================================