[N.C.] and {transpose} (for keyboard) cause warnings; and error in ChordPro output format

[gwyndaf]

Flagging as a possible bug, though I can work around it. Don't know if this relates to #254

Generating ChordPro output with keyboard config, when a song includes [N.C.] and {transpose} directive gives no output and and this error:

Can't call method "has_diagrams" on an undefined value at /usr/local/share/perl/5.38.2/ChordPro/Output/ChordPro.pm line 369.

I can easily avoid the error, and generate output, by adding --diagrams=none to the command, as I don't need diagrams defining in this case.

With PDF output, I'm fairly used to those same conditions generating just a warning:

Cannot parse/transpose chord "N.C."

That doesn't trouble me, but I thought an error and processing failure worth mentioning.