added null checks for arguments in MutableCredentials

Author: ldetmer

google-cloud-spanner/src/main/java/com/google/cloud/spanner/MutableCredentials.java

@@ -23,6 +23,7 @@
 import java.net.URI;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.Executor;
 import javax.annotation.Nonnull;
@@ -49,7 +50,9 @@ public MutableCredentials(ServiceAccountCredentials credentials) {
     this(credentials, SpannerOptions.SCOPES);
   }
 
-  public MutableCredentials(ServiceAccountCredentials credentials, @Nonnull Set<String> scopes) {
+  public MutableCredentials(@Nonnull ServiceAccountCredentials credentials, @Nonnull Set<String> scopes) {
+    Objects.requireNonNull(credentials, "credentials must not be null");
+    Objects.requireNonNull(scopes, "scopes must not be null");
     if (scopes.isEmpty()) {
       throw new IllegalArgumentException("Scopes must not be empty");
     }
@@ -60,13 +63,16 @@ public MutableCredentials(ServiceAccountCredentials credentials, @Nonnull Set<St
   /**
    * Replaces the current delegate with a newly scoped credentials instance.
    *
+   * Note any in-flight RPC may continue to use the old credentials.
+   *
    * <p>The provided {@link ServiceAccountCredentials} is scoped using the same scopes that were
    * supplied when this {@link MutableCredentials} instance was created.
    *
    * @param credentials the new base service account credentials to scope and use for client
    *     authorization.
    */
-  public void updateCredentials(ServiceAccountCredentials credentials) {
+  public void updateCredentials(@Nonnull ServiceAccountCredentials credentials) {
+    Objects.requireNonNull(credentials, "credentials must not be null");
     delegate = (ServiceAccountCredentials) credentials.createScoped(scopes);
   }
 

google-cloud-spanner/src/test/java/com/google/cloud/spanner/MutableCredentialsTest.java

@@ -19,6 +19,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
@@ -134,6 +135,31 @@ public void testCreateMutableCredentialsEmptyScopesThrowsError() {
     new MutableCredentials(initialCredentials, Collections.emptySet());
   }
 
+  @Test
+  public void testCreateMutableCredentialsNullCredentialsThrowsError() {
+    NullPointerException exception =
+        assertThrows(NullPointerException.class, () -> new MutableCredentials(null, scopes));
+    assertEquals("credentials must not be null", exception.getMessage());
+  }
+
+  @Test
+  public void testCreateMutableCredentialsNullScopesThrowsError() {
+    NullPointerException exception =
+        assertThrows(
+            NullPointerException.class, () -> new MutableCredentials(initialCredentials, null));
+    assertEquals("scopes must not be null", exception.getMessage());
+  }
+
+  @Test
+  public void testUpdateMutableCredentialsNullCredentialsThrowsError() throws IOException {
+    setupInitialCredentials();
+    MutableCredentials credentials = new MutableCredentials(initialCredentials, scopes);
+
+    NullPointerException exception =
+        assertThrows(NullPointerException.class, () -> credentials.updateCredentials(null));
+    assertEquals("credentials must not be null", exception.getMessage());
+  }
+
   private void validateInitialDelegatedCredentialsAreSet(
       MutableCredentials credentials, URI testUri) throws IOException {
     assertEquals(initialAuthType, credentials.getAuthenticationType());