Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
  +(nil 1)
  (let* ((v (+ (map-elt l "a" nil) 1))) (condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) (map-not-inplace (setq l (map-insert l "a" v)) v)))
  (let ((l (list (cons 'a 1)))) (let* ((v (+ (map-elt l "a" nil) 1))) (condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) (map-not-inplace (setq l (map-insert l "a" v)) v))) l)
  (progn (let ((l (list (cons 'a 1)))) (let* ((v (+ (map-elt l "a" nil) 1))) (condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) (map-not-inplace (setq l (map-insert l "a" v)) v))) l))
  eval((progn (let ((l (list (cons 'a 1)))) (let* ((v (+ (map-elt l "a" nil) 1))) (condition-case nil (with-no-warnings (map-put! l "a" v #'string=)) (map-not-inplace (setq l (map-insert l "a" v)) v))) l)) t)
  elisp--eval-last-sexp(t)
  eval-last-sexp(t)
  eval-print-last-sexp(nil)
  funcall-interactively(eval-print-last-sexp nil)
  call-interactively(eval-print-last-sexp nil nil)
  command-execute(eval-print-last-sexp)