wrong-type-argument error while enabling rustic-mode

[katyo]

After updating emacs to v31.0.50 I have the following error:

Debugger entered--Lisp error: (wrong-type-argument hash-table-p nil)
  flymake-mode(0)
  flymake-mode-off()
  run-hooks(change-major-mode-after-body-hook prog-mode-hook rust-mode-hook rustic-mode-hook)
  apply(run-hooks change-major-mode-after-body-hook (prog-mode-hook rust-mode-hook rustic-mode-hook))
  run-mode-hooks(rustic-mode-hook)
  ...

I commented out the following line to solve it:

rustic/rustic-flycheck.el

Line 215 in 1f4d6a3

(add-hook 'rustic-mode-hook 'flymake-mode-off)

I think It will be better do check that flymake really installed and enabled to disable it than this way.