wrong-type-argument stringp nil when executing the command with a custom interface

[robert-zaremba]

I'm calling go-imple with the following sequence:

• Receiver: k Keeper
• Interface: ugov.MsgServer

The command fails with:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  call-process(nil nil t nil "k Keeper" "ugov.MsgServer")
  apply(call-process nil nil t nil ("k Keeper" "ugov.MsgServer"))
  process-file(nil nil t nil "k Keeper" "ugov.MsgServer")
  go-impl--execute("k Keeper" "ugov.MsgServer")
  go-impl("k Keeper" "ugov.MsgServer")
  funcall-interactively(go-impl "k Keeper" "ugov.MsgServer")
  call-interactively(go-impl record nil)
  command-execute(go-impl record)
  execute-extended-command(nil "go-impl" nil)
  funcall-interactively(execute-extended-command nil "go-impl" nil)
  call-interactively(execute-extended-command nil nil)
  command-execute(execute-extended-command)

When running impl directly in the package directory, it outputs correctly a stub interface:

impl 'k Keeper' ugov.MsgServer

[kotatsuyaki]

Fired up Emacs to test this. git-gutter-fringe is working nicely with the built-in global-display-line-numbers-mode on Emacs 26.2.