Exception

The application raised an exception with the message:

    link: contract violation
      expected: stringish?
      given: '(img ((src "images/tfl-book-cover.gif")))
      in: the 1st argument of
          (->*
           (stringish?)
           (stringish? #:class stringish?)
           tagged-xexpr?)
      contract from: (function link)
      blaming: /Users/mb/git/bpt/pollen-require/bpt-elements.rkt
      at: /Users/mb/git/bpt/pollen-require/bpt-elements.rkt:44.18

Stack trace:

    raise-blame-error16 at:
      line 143, column 0, in file /Users/mb/git/racket/racket/collects/racket/contract/private/blame.rkt
    <unknown procedure> at:
      line 1570, column 30, in file /Users/mb/git/racket/racket/collects/racket/private/kw.rkt
    [running body] at:
      line #f, column #f, in file (submod /Users/mb/git/bpt/how-to-pay-for-this-book.html.pd pollen-inner)
    [traversing imports] at:
      line #f, column #f, in file /Users/mb/git/bpt/how-to-pay-for-this-book.html.pd
    find-in-main at:
      <unknown location>
    with-output-to-string at:
      line 125, column 0, in file /Users/mb/git/racket/racket/collects/racket/port.rkt
    core112 at:
      <unknown location>
    loop at:
      line 53, column 19, in file /Users/mb/git/racket/racket/collects/racket/private/map.rkt
    route-default at:
      line 206, column 0, in file /Users/mb/git/pollen/server-routes.rkt
    <unknown procedure> at:
      line 58, column 2, in file /Users/mb/git/racket/pkgs/web-server-pkgs/web-server-lib/web-server/dispatchers/dispatch-servlets.rkt
    <unknown procedure> at:
      line 112, column 8, in file /Users/mb/git/racket/pkgs/web-server-pkgs/web-server-lib/web-server/private/dispatch-server-unit.rkt