Support SetBenchmark(null) to disable the benchmark

Algorithm/QCAlgorithm.cs

@@ -1527,7 +1527,7 @@ public void SetBenchmark(string ticker)
         /// <summary>
         /// Sets the benchmark used for computing statistics of the algorithm to the specified symbol
         /// </summary>
-        /// <param name="symbol">symbol to use as the benchmark</param>
+        /// <param name="symbol">symbol to use as the benchmark, null to disable the benchmark</param>
         [DocumentationAttribute(TradingAndOrders)]
         [DocumentationAttribute(SecuritiesAndPortfolio)]
         [DocumentationAttribute(Indicators)]
@@ -1538,6 +1538,13 @@ public void SetBenchmark(Symbol symbol)
                 throw new InvalidOperationException(Messages.QCAlgorithm.SetBenchmarkAlreadyInitialized());
             }
 
+            if (symbol == null)
+            {
+                // Equivalent to no benchmark
+                Benchmark = new FuncBenchmark(_ => 0);
+                return;
+            }
+
             // Create our security benchmark
             Benchmark = SecurityBenchmark.CreateInstance(Securities, symbol);
         }

Tests/Algorithm/AlgorithmBenchmarkTests.cs

@@ -149,6 +149,38 @@ public void PythonSetBenchmarkThrowsDescriptiveErrorForUnsupportedBenchmarkType(
             }
         }
 
+        [TestCase(Language.CSharp)]
+        [TestCase(Language.Python)]
+        public void NullBenchmarkDisablesTheBenchmark(Language language)
+        {
+            var algorithm = new QCAlgorithm();
+            var dataManager = new DataManagerStub(algorithm, new MockDataFeed());
+            algorithm.SubscriptionManager.SetDataManager(dataManager);
+
+            if (language == Language.CSharp)
+            {
+                algorithm.SetBenchmark((Symbol)null);
+            }
+            else
+            {
+                using var _ = Py.GIL();
+                using var module = PyModule.FromString(nameof(NullBenchmarkDisablesTheBenchmark), @"
+def set_benchmark(algorithm):
+    algorithm.set_benchmark(None)
+");
+                using var pyAlgorithm = algorithm.ToPython();
+                using var setBenchmark = module.GetAttr("set_benchmark");
+                setBenchmark.Invoke(pyAlgorithm);
+            }
+
+            algorithm.PostInitialize();
+
+            // The default brokerage model benchmark is not used and no benchmark security is added
+            Assert.IsInstanceOf<FuncBenchmark>(algorithm.Benchmark);
+            Assert.AreEqual(0m, algorithm.Benchmark.Evaluate(new DateTime(2024, 1, 2)));
+            Assert.IsEmpty(algorithm.Securities);
+        }
+
         [Test]
         public void BenchmarkIsNotInitializeWithCustomSecurityInitializer()
         {