Fix registrar security console

The registrar security console failed because it assumed the email is a
required field for the registrar, but it isn't (at least - create_registrar
doesn't require an email, and update_registrar lets you remove the email).

Fixed by allowing it to *remain* unset if it was unset originally, but if it was set - it's required.

There are more fixes needed, but they aren't related to the email, so they will wait for the next CL

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191623034

javatests/google/registry/server/RegistryTestServer.java

@@ -88,6 +88,8 @@ public final class RegistryTestServer {
       route("/registrar", google.registry.module.frontend.FrontendServlet.class),
       route("/registrar-settings",
           google.registry.module.frontend.FrontendServlet.class),
+      route("/registrar-premium-price-ack",
+          google.registry.module.frontend.FrontendServlet.class),
       route("/registrar-payment",
           google.registry.module.frontend.FrontendServlet.class),
       route("/registrar-payment-setup",

javatests/google/registry/ui/server/registrar/RegistrarSettingsActionTest.java

@@ -16,6 +16,7 @@ package google.registry.ui.server.registrar;
 
 import static com.google.common.truth.Truth.assertThat;
 import static google.registry.testing.DatastoreHelper.loadRegistrar;
+import static google.registry.testing.DatastoreHelper.persistResource;
 import static google.registry.testing.JUnitBackports.assertThrows;
 import static google.registry.testing.TaskQueueHelper.assertNoTasksEnqueued;
 import static google.registry.testing.TaskQueueHelper.assertTasksEnqueued;
@@ -98,6 +99,16 @@ public class RegistrarSettingsActionTest extends RegistrarSettingsActionTestCase
     assertNoTasksEnqueued("sheet");
   }
 
+  @Test
+  public void testUpdate_emptyJsonObject_emailFieldNotRequiredWhenEmpty() throws Exception {
+    persistResource(loadRegistrar(CLIENT_ID).asBuilder().setEmailAddress(null).build());
+
+    Map<String, Object> response = action.handleJsonRequest(ImmutableMap.of(
+        "op", "update",
+        "args", ImmutableMap.of()));
+    assertThat(response).containsEntry("status", "SUCCESS");
+  }
+
   @Test
   public void testUpdate_badEmail_errorEmailField() throws Exception {
     Map<String, Object> response = action.handleJsonRequest(ImmutableMap.of(

javatests/google/registry/ui/server/registrar/RegistrarSettingsActionTestCase.java

@@ -106,8 +106,12 @@ public class RegistrarSettingsActionTestCase {
     when(rsp.getWriter()).thenReturn(new PrintWriter(writer));
     when(req.getContentType()).thenReturn("application/json");
     when(req.getReader()).thenReturn(createJsonPayload(ImmutableMap.of("op", "read")));
+    // We mock getRegistrarForAuthResult to reload the registrar each time it's called. Otherwise -
+    // the result is out of date after mutations.
+    // (for example, if someone wants to change the registrar to prepare for a test, the function
+    // would still return the old value)
     when(sessionUtils.getRegistrarForAuthResult(req, action.authResult))
-        .thenReturn(loadRegistrar(CLIENT_ID));
+        .thenAnswer(x -> loadRegistrar(CLIENT_ID));
     when(modulesService.getVersionHostname("backend", null)).thenReturn("backend.hostname");
   }