The application raised an exception with the message:

car: expects argument of type <pair>; given ()

Stack trace:

<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 57, column 2, in file /opt/lib/plt/collects/web-server/dispatchers/dispatch-servlets.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
select-handler/no-breaks at:
  line 170, column 2, in file /opt/lib/plt/collects/scheme/private/more-scheme.ss
select-handler/no-breaks at:
  line 170, column 2, in file /opt/lib/plt/collects/scheme/private/more-scheme.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
<unknown procedure> at:
  line 1348, column 3, in file /opt/lib/plt/collects/scheme/private/contract-arrow.ss
connection-loop at:
  line 62, column 2, in file /opt/lib/plt/collects/web-server/private/dispatch-server-unit.ss