diff --git a/server.py b/server.py
index 4f22efb68..8ca6622f6 100644
--- a/server.py
+++ b/server.py
@@ -795,10 +795,13 @@ class PromptServer():
             result still returns ``{}`` with HTTP 200 rather than 404 — absence
             of an error is a valid answer for this endpoint.
             """
+            # Coalesce empty-string query values to None so `?source=` (param
+            # present but blank) is treated the same as the param being absent
+            # — rather than filtering for entries whose source is literally "".
             grouped = nodes.filter_node_startup_errors(
-                source=request.query.get("source"),
-                module_name=request.query.get("module_name"),
-                pack_id=request.query.get("pack_id"),
+                source=request.query.get("source") or None,
+                module_name=request.query.get("module_name") or None,
+                pack_id=request.query.get("pack_id") or None,
             )
             return web.json_response(grouped)
 
diff --git a/tests-unit/node_startup_errors_test.py b/tests-unit/node_startup_errors_test.py
index cf66f8e3b..0afe01fc4 100644
--- a/tests-unit/node_startup_errors_test.py
+++ b/tests-unit/node_startup_errors_test.py
@@ -218,6 +218,11 @@ def test_filter_node_startup_errors_source_filter():
     assert set(grouped["comfy_extras"]) == {"B"}
     # Non-matching source filter returns an empty dict, not an error.
     assert nodes.filter_node_startup_errors(source="nope") == {}
+    # An explicit empty-string filter is treated as a real value (matches
+    # entries whose source is literally ""), NOT silently as "no filter".
+    # The HTTP route layer is responsible for coalescing `?source=` to None
+    # before calling this helper; this assertion locks that contract in.
+    assert nodes.filter_node_startup_errors(source="") == {}
 
 
 def test_filter_node_startup_errors_module_name_filter():