I'm having the same issue. I can't add a delegate class through the text input field in the Blue Ocean UI. Whatever you enter is interpreted as String - not as a class.
using Blue Ocean 1.4.2
Reopening this issue, since it seems there is no possibility to enter a valid value into the "Delegate" text input field.
Max von Preuschen - please open a new JIRA in the blueocean component.
Bulk closing resolved issues.