fix(worker): allow Nexus-only workers

src/Temporalio/Worker/TemporalWorker.cs

@@ -63,16 +63,18 @@ public TemporalWorker(IWorkerClient client, TemporalWorkerOptions options)
 
                 var bridgeClient = client.BridgeClientProvider.BridgeClient ??
                                    throw new InvalidOperationException("Cannot use unconnected lazy client for worker");
+
+                if (options.Activities.Count == 0 && options.Workflows.Count == 0 && options.NexusServices.Count == 0)
+                {
+                    throw new ArgumentException("Must have at least one workflow, activity, or Nexus service");
+                }
+
                 BridgeWorker = new(
                     (Bridge.Client)bridgeClient,
                     client.Options.Namespace,
                     options,
                     loggerFactory,
                     client.Options.Plugins);
-                if (options.Activities.Count == 0 && options.Workflows.Count == 0)
-                {
-                    throw new ArgumentException("Must have at least one workflow and/or activity");
-                }
 
                 MetricMeter = MetricMeterBridge.LazyFromRuntime(BridgeWorker.Runtime);
 
@@ -128,6 +130,11 @@ public TemporalWorker(IWorkerClient client, TemporalWorkerOptions options)
                         DeploymentOptions: options.DeploymentOptions));
                 }
 
+                if (options.NexusServices.Count > 0)
+                {
+                    nexusWorker = new(this);
+                }
+
                 disposer = new Disposer(activityWorker, BridgeWorker, workflowTracingEventListenerEnabled);
             }
             catch (Exception)
@@ -140,10 +147,6 @@ public TemporalWorker(IWorkerClient client, TemporalWorkerOptions options)
                 }
                 throw;
             }
-            if (options.NexusServices.Count > 0)
-            {
-                nexusWorker = new(this);
-            }
         }
 
         /// <summary>

tests/Temporalio.Tests/Worker/GeneralWorkerTests.cs

@@ -12,6 +12,15 @@ public GeneralWorkerTests(ITestOutputHelper output, WorkflowEnvironment env)
     {
     }
 
+    [Fact]
+    public void Constructor_NoTaskTypes_Throws()
+    {
+        var exc = Assert.Throws<ArgumentException>(() =>
+            new TemporalWorker(
+                Env.Client,
+                new TemporalWorkerOptions($"tq-{Guid.NewGuid()}")));
+    }
+
     [Fact]
     public async Task ExecuteAsync_PropagatesException()
     {