Make Registrar load methods return Optionals instead of Nullables

This makes the code more understandable from callsites, and also forces
users of this function to deal with the situation where the registrar
with a given client ID might not be present (it was previously silently
NPEing from some of the callsites).

This also adds a test helper method loadRegistrar(clientId) that retains
the old functionality for terseness in tests. It also fixes some instances
of using the load method with the wrong cachedness -- some uses in high-
traffic situations (WHOIS) that should have caching, but also low-traffic
reporting that don't benefit from caching so might as well always be
current.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=162990468

java/google/registry/tools/PublishDetailReportCommand.java

@@ -14,7 +14,7 @@
 
 package google.registry.tools;
 
-import static com.google.common.base.Preconditions.checkNotNull;
+import static google.registry.util.PreconditionsUtils.checkArgumentPresent;
 
 import com.beust.jcommander.Parameter;
 import com.beust.jcommander.Parameters;
@@ -34,7 +34,7 @@ public class PublishDetailReportCommand extends ConfirmingCommand
       names = "--registrar_id",
       description = "Client identifier of the registrar to publish the report for",
       required = true)
-  private String registrarId;
+  private String clientId;
 
   @Parameter(
       names = "--report_name",
@@ -73,8 +73,9 @@ public class PublishDetailReportCommand extends ConfirmingCommand
     // TODO(b/18611424): Fix PublishDetailReportAction to take fewer error-prone parameters.
     gcsFolderPrefix =
         (gcsFolder.isEmpty() || gcsFolder.endsWith("/")) ? gcsFolder : gcsFolder + "/";
-    Registrar registrar = checkNotNull(
-        Registrar.loadByClientId(registrarId), "Registrar with ID %s not found", registrarId);
+    Registrar registrar =
+        checkArgumentPresent(
+            Registrar.loadByClientId(clientId), "Registrar with ID %s not found", clientId);
     driveFolderUrl = String.format(DRIVE_FOLDER_URL_TEMPLATE, registrar.getDriveFolderId());
   }
 
@@ -82,7 +83,7 @@ public class PublishDetailReportCommand extends ConfirmingCommand
   protected String prompt() {
     String gcsFile = String.format("gs://%s/%s%s", gcsBucket, gcsFolderPrefix, reportName);
     return "Publish detail report:\n"
-        + " - Registrar: " + registrarId + "\n"
+        + " - Registrar: " + clientId + "\n"
         + " - Drive folder: " + driveFolderUrl + "\n"
         + " - GCS file: " + gcsFile;
   }
@@ -90,7 +91,7 @@ public class PublishDetailReportCommand extends ConfirmingCommand
   @Override
   protected String execute() throws Exception {
     final ImmutableMap<String, String> params = ImmutableMap.of(
-        PublishDetailReportAction.REGISTRAR_ID_PARAM, registrarId,
+        PublishDetailReportAction.REGISTRAR_ID_PARAM, clientId,
         PublishDetailReportAction.DETAIL_REPORT_NAME_PARAM, reportName,
         PublishDetailReportAction.GCS_FOLDER_PREFIX_PARAM, gcsFolderPrefix,
         PublishDetailReportAction.GCS_BUCKET_PARAM, gcsBucket);