Check for null error stream (#2249)

core/src/main/java/google/registry/request/UrlConnectionUtils.java

@@ -50,6 +50,8 @@ public final class UrlConnectionUtils {
     try (InputStream is =
         responseCode < 400 ? connection.getInputStream() : connection.getErrorStream()) {
       return ByteStreams.toByteArray(is);
+    } catch (NullPointerException e) {
+      return new byte[] {};
     }
   }
 

core/src/test/java/google/registry/request/UrlConnectionUtilsTest.java

@@ -29,6 +29,7 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.when;
 
+import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.util.Arrays;
 import java.util.List;
@@ -104,4 +105,21 @@ public class UrlConnectionUtilsTest {
             "Multipart data contains autogenerated boundary: "
                 + "------------------------------AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
   }
+
+  @Test
+  void testErrorStream() throws Exception {
+    HttpsURLConnection connection = mock(HttpsURLConnection.class);
+    when(connection.getResponseCode()).thenReturn(400);
+    when(connection.getErrorStream())
+        .thenReturn(new ByteArrayInputStream("Failure".getBytes(UTF_8)));
+    assertThat(UrlConnectionUtils.getResponseBytes(connection))
+        .isEqualTo("Failure".getBytes(UTF_8));
+  }
+
+  @Test
+  void testErrorStream_null() throws Exception {
+    HttpsURLConnection connection = mock(HttpsURLConnection.class);
+    when(connection.getResponseCode()).thenReturn(400);
+    assertThat(UrlConnectionUtils.getResponseBytes(connection)).isEmpty();
+  }
 }