Fix XPENDING empty-PEL reply schema and stop req-res-log-validator masking schema errors

src/commands/xpending.json

@@ -113,6 +113,30 @@
                             }
                         }
                     ]
+                },
+                {
+                    "description": "Summary form when there are no pending messages.",
+                    "type": "array",
+                    "minItems": 4,
+                    "maxItems": 4,
+                    "items": [
+                        {
+                            "description": "Total number of pending messages",
+                            "const": 0
+                        },
+                        {
+                            "description": "Minimal pending entry ID",
+                            "type": "null"
+                        },
+                        {
+                            "description": "Maximal pending entry ID",
+                            "type": "null"
+                        },
+                        {
+                            "description": "Consumers with pending messages",
+                            "type": "null"
+                        }
+                    ]
                 }
             ]
         },

tests/unit/type/stream-cgroups.tcl

@@ -98,6 +98,12 @@ start_server {
         assert {[llength $pending] == 4}
     }
 
+    test {XPENDING only group with an empty PEL} {
+        r XGROUP CREATE mystream emptygroup $
+        assert_equal {0 {} {} {}} [r XPENDING mystream emptygroup]
+        r XGROUP DESTROY mystream emptygroup
+    }
+
     test {XPENDING with IDLE} {
         after 20
         set pending [r XPENDING mystream mygroup IDLE 99999999 - + 10 consumer-1]

utils/req-res-log-validator.py

@@ -236,7 +236,11 @@ def process_file(docs, path):
                    print("Response: (unprintable)")
                 print(f"Schema: {json.dumps(req.schema, indent=2)}")
                 print(traceback.format_exc())
-                raise
+                # jsonschema exceptions hold a reference to a TypeChecker lambda in
+                # jsonschema._types, which cannot be pickled. process_file runs in a
+                # multiprocessing pool worker, so re-raising one makes the parent report
+                # MaybeEncodingError/PicklingError instead of the validation failure.
+                raise RuntimeError(f"JSON schema validation error on {path}: {err}")
 
     return command_counter