fix: Allow quota project to be used in combination with null credentials (#1688)

Author: irock

gax-java/gax/src/main/java/com/google/api/gax/rpc/ClientContext.java

@@ -167,7 +167,7 @@ public static ClientContext create(StubSettings settings) throws IOException {
 
     Credentials credentials = settings.getCredentialsProvider().getCredentials();
 
-    if (settings.getQuotaProjectId() != null) {
+    if (settings.getQuotaProjectId() != null && credentials != null) {
       // If the quotaProjectId is set, wrap original credentials with correct quotaProjectId as
       // QuotaProjectIdHidingCredentials.
       // Ensure that a custom set quota project id takes priority over one detected by credentials.

gax-java/gax/src/test/java/com/google/api/gax/rpc/ClientContextTest.java

@@ -41,6 +41,7 @@
 import com.google.api.gax.core.ExecutorProvider;
 import com.google.api.gax.core.FixedCredentialsProvider;
 import com.google.api.gax.core.FixedExecutorProvider;
+import com.google.api.gax.core.NoCredentialsProvider;
 import com.google.api.gax.rpc.mtls.MtlsProvider;
 import com.google.api.gax.rpc.mtls.MtlsProvider.MtlsEndpointUsagePolicy;
 import com.google.api.gax.rpc.testing.FakeChannel;
@@ -533,6 +534,26 @@ public Credentials getCredentials() throws IOException {
     assertThat(clientContext.getCredentials().getRequestMetadata(null)).isEqualTo(metaData);
   }
 
+  @Test
+  public void testQuotaProjectId_worksWithNullCredentials() throws IOException {
+    final String QUOTA_PROJECT_ID = "quota_project_id";
+
+    final InterceptingExecutor executor = new InterceptingExecutor(1);
+    final FakeTransportChannel transportChannel = FakeTransportChannel.create(new FakeChannel());
+    final FakeTransportProvider transportProvider =
+        new FakeTransportProvider(
+            transportChannel, executor, true, null, Mockito.mock(Credentials.class));
+
+    final FakeClientSettings.Builder settingsBuilder = new FakeClientSettings.Builder();
+
+    settingsBuilder
+        .setTransportChannelProvider(transportProvider)
+        .setCredentialsProvider(NoCredentialsProvider.create())
+        .setQuotaProjectId(QUOTA_PROJECT_ID);
+
+    assertThat(ClientContext.create(settingsBuilder.build()).getCredentials()).isNull();
+  }
+
   @Test
   public void testUserAgentInternalOnly() throws Exception {
     TransportChannelProvider transportChannelProvider =