
  -spec is_map_key(Key, Map) -> boolean() when Key :: term(), Map :: map().

Since:
  OTP 21.0

  Returns true if map Map contains Key and returns false if
  it does not contain the Key.

  The call fails with a {badmap,Map} exception if Map is not a
  map.

  Example:

    > Map = #{"42" => value}.
    #{"42" => value}
    > is_map_key("42",Map).
    true
    > is_map_key(value,Map).
    false

  Allowed in guard tests.
