FormField marks the Title constructor argument as optional, and DatalessField does not override the __construct method. HeaderField on the other hand goes against the grain of FormFields as a whole and requires the Title field, seemingly for no good reason (at least, not that the commit message for a68ba38478 indicates) - this seems like an accidental ommision. This commit looks to reinstate the optionality of this constructor argument for consistency's sake.
Plus it broke a module I was investigating.
Daniel Hensby
Dylan Wagstaff
Damian Mooyman
Sam Minnee