diff --git a/backend/packages/harness/deerflow/agents/memory/backends/deermem/deermem/core/message_processing.py b/backend/packages/harness/deerflow/agents/memory/backends/deermem/deermem/core/message_processing.py
index e482cabe1f..d9d55aee4a 100644
--- a/backend/packages/harness/deerflow/agents/memory/backends/deermem/deermem/core/message_processing.py
+++ b/backend/packages/harness/deerflow/agents/memory/backends/deermem/deermem/core/message_processing.py
@@ -97,6 +97,13 @@ def load_patterns(name: str, *, patterns_dir: str | None = None) -> list[re.Patt
 def extract_message_text(message: Any) -> str:
     """Extract plain text from message content for filtering and signal detection."""
     content = getattr(message, "content", "")
+    if content is None:
+        # ``str(None)`` is the truthy literal ``"None"``, so a content-less
+        # message would survive every downstream ``text if text else ...``
+        # fallback and be reported as real user text. Keep this in step with
+        # ``deerflow/utils/messages.py:message_content_to_text`` and the mem0
+        # copy of this helper, which both return "" here.
+        return ""
     if isinstance(content, list):
         text_parts: list[str] = []
         for part in content:
diff --git a/backend/tests/test_message_processing_signals.py b/backend/tests/test_message_processing_signals.py
index 5d32f1203b..33ecaffec2 100644
--- a/backend/tests/test_message_processing_signals.py
+++ b/backend/tests/test_message_processing_signals.py
@@ -137,3 +137,19 @@ def test_prepare_update_returns_new_signals_after_swap(tmp_path) -> None:
     _filtered, signals = r
     assert "preference" in signals
     assert len(_filtered) == 2  # not trivial -> kept
+
+
+# ── extract_message_text: content shapes ───────────────────────────────────
+
+
+def test_extract_message_text_treats_none_as_empty() -> None:
+    """A content-less message must not become the literal string ``"None"``.
+
+    ``str(None)`` is truthy, so the naive fallback would hand ``"None"`` to
+    signal detection and to the memory-update prompt as if it were real user
+    text. Mirrors ``utils/messages.py:message_content_to_text`` and
+    ``test_mem0_memory_backend.py::test_extract_message_text_treats_none_as_empty``.
+    """
+    msg = _human("")
+    msg.content = None
+    assert extract_message_text(msg) == ""