From f52dc2a8d81e9814ae72607679e8e724577ff54d Mon Sep 17 00:00:00 2001
From: guglielmoc <guglielmoc@google.com>
Date: Tue, 10 Nov 2026 10:16:03 +0000
Subject: [PATCH] Allow nil params for ListRoots

---
 mcp/protocol.go      |  7 +++++--
 mcp/protocol_test.go | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/mcp/protocol.go b/mcp/protocol.go
index 8ca96b24e..d78d25061 100644
--- a/mcp/protocol.go
+++ b/mcp/protocol.go
@@ -128,9 +128,12 @@ func (m *InputRequestMap) UnmarshalJSON(data []byte) error {
 			}
 			result[k] = &p
 		case methodListRoots:
+			// For a roots/list request, params are optional.
 			var p ListRootsParams
-			if err := internaljson.Unmarshal(raw.Params, &p); err != nil {
-				return err
+			if len(raw.Params) > 0 {
+				if err := internaljson.Unmarshal(raw.Params, &p); err != nil {
+					return err
+				}
 			}
 			result[k] = &p
 		default:
diff --git a/mcp/protocol_test.go b/mcp/protocol_test.go
index cd2ae94eb..86f869e86 100644
--- a/mcp/protocol_test.go
+++ b/mcp/protocol_test.go
@@ -1222,6 +1222,21 @@ func TestInputRequestMapJSON(t *testing.T) {
 			t.Error("Unmarshal succeeded, want an error for a null input request")
 		}
 	})
+
+	// roots/list params are optional, so a request without them must not fail
+	// decoding the whole result.
+	for _, params := range []string{``, `,"params":null`} {
+		t.Run("roots/list without params"+params, func(t *testing.T) {
+			var got CallToolResult
+			data := `{"content":[],"inputRequests":{"r1":{"method":"roots/list"` + params + `}}}`
+			if err := json.Unmarshal([]byte(data), &got); err != nil {
+				t.Fatalf("Unmarshal(%s) = %v, want nil", data, err)
+			}
+			if p, ok := got.InputRequests["r1"].(*ListRootsParams); !ok || p == nil {
+				t.Errorf("InputRequests[r1] = %#v, want non-nil *ListRootsParams", got.InputRequests["r1"])
+			}
+		})
+	}
 }
 
 func TestInputResponseMapJSON(t *testing.T) {