Type unions don't display well in error messages

[cgay]

sources/dfmc/reader/lexer.dylan:880.10-64: Serious warning - 
Invalid type for argument string-or-character in call to 
whitespace? (string-or-character :: <string-or-char>) => (whitespace? :: <boolean>): 
 <simple-byte-vector> supplied, {model-object :: <union>} expected.
               ------------------------------------------------------
          if (~whitespace?(contents, start: bpos, end: first-newline))
               ------------------------------------------------------

The {model-object :: <union>} in that message is defined in the strings library like this:

define constant <string-or-char> = type-union(<string>, <character>);

So it should probably say "... type-union(<string>, <character>) expected."