Issue Summary

Project boards do not load and throw 500 error if there is a custom field configured on the Jira instance that has a blank field for a name.

Steps to Reproduce

1. Create a custom field with any name
2. Edit custom field, and edit the name of the custom field to only have a blank "space" character and save changes
3. Try to load a project board - the board will not load and throw a 500 error

Expected Results

Jira should prevent users from editing an existing custom field's name to " " (a blank space character) - this breaks the boards and results in a 500 error

Actual Results

It is possible to edit a custom field's name, and change it to " " (a blank space)

The below exception is thrown in the xxxxxxx.log file:

Caused by: com.atlassian.jira.util.dbc.Assertions$BlankStringArgumentException: names[0] should not be empty!
	at com.atlassian.jira.util.dbc.Assertions.containsNoBlanks(Assertions.java:161)
	at com.atlassian.jira.issue.search.ClauseNames.<init>(ClauseNames.java:43)
	at com.atlassian.jira.issue.search.DefaultClauseNamesService.lambda$forCustomField$2(DefaultClauseNamesService.java:48)
	at com.atlassian.workcontext.metrics.Timer.time(Timer.java:208)
	at com.atlassian.jira.issue.search.DefaultClauseNamesService.forCustomField(DefaultClauseNamesService.java:48)
	at com.atlassian.jira.issue.fields.ImmutableCustomField.getClauseNames(ImmutableCustomField.java:565)

Workaround

Rename the affected custom field so that it has a name and save the changes. This should allow the boards to load as expected.