The error trace is shown below.
Debugger entered--Lisp error: (wrong-type-argument char-or-string-p nil)
quail-help("korean-hangul")
eval((quail-help "korean-hangul") nil)
eval-last-sexp-1(t)
eval-last-sexp(t)
eval-print-last-sexp()
call-interactively(eval-print-last-sexp nil nil)
recursive-edit()
debug(error (wrong-type-argument char-or-string-p nil))
quail-help("korean-hangul")
eval((quail-help "korean-hangul") nil)
eval-last-sexp-1(t)
eval-last-sexp(t)
eval-print-last-sexp()
call-interactively(eval-print-last-sexp nil nil)
recursive-edit()
debug(error (void-function quail-help))
(quail-help "korean-hangul")
eval((quail-help "korean-hangul") nil)
eval-last-sexp-1(t)
eval-last-sexp(t)
eval-print-last-sexp()
call-interactively(eval-print-last-sexp nil nil)
recursive-edit()
debug(error (void-function quail-help))
(quail-help (quote korean-hangul))
eval((quail-help (quote korean-hangul)) nil)
eval-last-sexp-1(t)
eval-last-sexp(t)
eval-print-last-sexp()
call-interactively(eval-print-last-sexp nil nil)