Add unit test to check that AnyRequest handles missing parameters

Sources/MCP/Base/Messages.swift

@@ -11,6 +11,12 @@ public struct Empty: NotRequired, Hashable, Codable, Sendable {
     public init() {}
 }
 
+extension Value: NotRequired {
+    public init() {
+        self = .null
+    }
+}
+
 // MARK: -
 
 /// A method that can be used to send requests and receive responses.

Tests/MCPTests/RequestTests.swift

@@ -260,4 +260,49 @@ struct RequestTests {
             from: withCursor.data(using: .utf8)!)
         #expect(decodedWithCursor.params.cursor == "next-page")
     }
+
+    @Test("AnyRequest parameters request decoding - without params")
+    func testAnyRequestParametersRequestDecodingWithoutParams() throws {
+        // Test decoding when params field is missing
+        let jsonString = """
+            {"jsonrpc":"2.0","id":1,"method":"ping"}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(AnyRequest.self, from: data)
+
+        #expect(decoded.id == 1)
+        #expect(decoded.method == Ping.name)
+    }
+
+    @Test("AnyRequest parameters request decoding - with null params")
+    func testAnyRequestParametersRequestDecodingWithNullParams() throws {
+        // Test decoding when params field is null
+        let jsonString = """
+            {"jsonrpc":"2.0","id":1,"method":"ping","params":null}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<Ping>.self, from: data)
+
+        #expect(decoded.id == 1)
+        #expect(decoded.method == Ping.name)
+    }
+
+    @Test("AnyRequest parameters request decoding - with empty params")
+    func testAnyRequestParametersRequestDecodingWithEmptyParams() throws {
+        // Test decoding when params field is null
+        let jsonString = """
+            {"jsonrpc":"2.0","id":1,"method":"ping","params":{}}
+            """
+        let data = jsonString.data(using: .utf8)!
+
+        let decoder = JSONDecoder()
+        let decoded = try decoder.decode(Request<Ping>.self, from: data)
+
+        #expect(decoded.id == 1)
+        #expect(decoded.method == Ping.name)
+    }
 }