Make async flow logic handle missing client transaction IDs

Per EPP RFC 5730, the <clTRID> element is optional. However, we weren't handling
it not being specified in asynchronous contact/host deletions because we were
adding it directly as a parameter value on a task, which does not allow null and
thus threw a NullPointerException.

This fixes handling for nulls (the parameter isn't set at all) and adds a test.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=194123259

java/google/registry/tools/AllocateDomainCommand.java

@@ -134,7 +134,7 @@ final class AllocateDomainCommand extends MutatingEppToolCommand {
                             "Could not find any history entries for domain application %s",
                             application.getRepoId());
                     String clientTransactionId =
-                        emptyToNull(history.getTrid().getClientTransactionId());
+                        emptyToNull(history.getTrid().getClientTransactionId().orElse(null));
                     Period period = checkNotNull(extractPeriodFromXml(history.getXmlBytes()));
                     checkArgument(period.getUnit() == Period.Unit.YEARS);
                     ImmutableMap.Builder<String, String> contactsMapBuilder =