Knowledge base articles are not searchable on Jira Service Desk with Japanese (non-Latin) keyword

Summary

Scenario 1

Related knowledge base articles are not shown in issue pages on Jira Service Desk if the issue summary is written only with multibyte character.

Scenario 2

Knowledge base articles are not searchable on Jira Service Desk with multibyte characters.

Environment

• Confluence 6.12.0
• Jira Service Desk 3.15.3

Steps to Reproduce

Scenario 1

1. Integrate Confluence with Jira Service Desk
2. Create a service desk project
3. Create an issue with Japanese summary in the project
4. Navigate to the issue page and see Related knowledge base articles section

Scenario 2

1. Integrate Confluence with Jira Service Desk
2. Create a service desk project
3. Create a knowledge base article which contains both Japanese and English
4. Navigate to customer portal and insert Japanese keyword in the search bar

Expected Results

Scenario 1

No error was shown.

Scenario 2

The knowledge base article should be suggested on the portal.

Actual Results

Scenario 1

The following error was shown on the UI.

The knowledge base server returned an error response.

We can see the error below in atlassian-confluence.log as well when reproducing this bug.

2018-10-29 08:35:37,057 ERROR [http-nio-8090-exec-2] [common.error.jersey.ThrowableExceptionMapper] toResponse Uncaught exception thrown by REST service: Raw query is required.
 -- url: /rest/knowledge-base/1.0/search/SER | traceId: 4de6e1e060d9ea2a | userName: admin
java.lang.IllegalArgumentException: Raw query is required.
	at com.atlassian.confluence.search.v2.query.TextFieldQuery.<init>(TextFieldQuery.java:41)
	at com.atlassian.confluence.plugins.search.api.model.SearchQueryParameters$SearchV2Query.<init>(SearchQueryParameters.java:151)
	at com.atlassian.confluence.plugins.search.api.model.SearchQueryParameters.toSearchV2Query(SearchQueryParameters.java:123)
	at com.atlassian.confluence.plugins.confluence_kb_space_blueprint.rest.SearchResource.publishKbSearchPerformedEvent(SearchResource.java:291)
	at com.atlassian.confluence.plugins.confluence_kb_space_blueprint.rest.SearchResource.lambda$executeSearch$0(SearchResource.java:272)
	at com.atlassian.sal.core.transaction.HostContextTransactionTemplate$1.doInTransaction(HostContextTransactionTemplate.java:21)
	at com.atlassian.sal.spring.component.SpringHostContextAccessor$1.doInTransaction(SpringHostContextAccessor.java:71)
	at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133)
...

Scenario 2

The knowledge base article was not suggested.
The same knowledge base was suggested as expected with English keyword.

English:

Japanese:

The same exception was shown in the log when reproducing this problem.

Notes

This is not a Jira Service Desk bug but a Confluence bug.

• This problem couldn't reproduce with Confluence 6.10.x
• When opening a Jira issue page (Scenario 1), JSD sent the following request to Confluence but there seems to be nothing wrong with it

  http(s)://<confluence-base-url>/knowledge-base/1.0/search/<SPACE-KEY>?type=page&queryString=<ENCODED-ISSUE-SUMMARY>&permissionCheckedUser=<USER>&highlight=false&xoauth_requestor_id=<USER>
  

As described in the above, this problem could be reproduced if the issue summary is written only with multibyte characters.

Issue Summary	Is reproduced? ( means reproducible)
テスト
test
テストtest
testテスト

This is also reproducible with other non-Latin character-sets and has been verified to occur with Cyrillic characters as well

Workaround

Please make the issue summary contain one or more English characters.