Add a field to the InvalidParam exception.

Use it in Ship.pm for documenting bad requested classes, and test
its use.

lib/WebGUI/Exception.pm

@@ -28,6 +28,7 @@ use Exception::Class (
     'WebGUI::Error::InvalidParam' => {
         isa             => 'WebGUI::Error',
         description     => "Expected to get a param we didn't get.",
+        fields          => ["param"],
         },
     'WebGUI::Error::ObjectNotFound' => {
         isa             => 'WebGUI::Error',
@@ -120,6 +121,10 @@ The object type we got.
 
 Used when an invalid parameter is passed into a subroutine.
 
+=head3 param
+
+Used to return the bad parameter, if present.
+
 =head2 WebGUI::Error::ObjectNotFound
 
 Used when an object is trying to be retrieved, but does not exist. ISA WebGUI::Error.

lib/WebGUI/Shop/Ship.pm

@@ -56,7 +56,7 @@ sub create {
     my $requestedClass = shift;
     WebGUI::Error::InvalidParam->throw(error => q{Must provide a class to create an object})
         unless defined $requestedClass;
-    WebGUI::Error::InvalidParam->throw(error => qq{The requested class $requestedClass is not enabled in your WebGUI configuration file})
+    WebGUI::Error::InvalidParam->throw(error => q{The requested class is not enabled in your WebGUI configuration file}, param => $requestedClass)
         unless isIn($requestedClass, @{ WebGUI::Shop::Ship->getDrivers($session) } );
     my $options = shift;
     WebGUI::Error::InvalidParam->throw(error => q{You must pass a hashref of options to create a new ShipDriver object})

t/Shop/Ship.t

@@ -109,7 +109,8 @@ isa_ok($e, 'WebGUI::Error::InvalidParam', 'create croaks without a configured cl
 cmp_deeply(
     $e,
     methods(
-        error => 'The requested class WebGUI::Shop::ShipDriver::FreeShipping is not enabled in your WebGUI configuration file',
+        error => 'The requested class is not enabled in your WebGUI configuration file',
+        param => 'WebGUI::Shop::ShipDriver::FreeShipping',
     ),
     'create croaks without a configured class',
 );