Create List ContentType programmatically : Sharepoint

Hi,
In WSS 3.0 / Moss 2007 I want to programmatically create a list level (not
site level) content type using list level (and again not site level)
columns.
Adding the content type to a list seems straight forward the difficulty
seems to be adding a field/column to the contentType.
Below is the code I tried. The code gives me a System.ArgumentNullException
error stating: {"Value cannot be null.\r\nParameter name: g"} on the line.
SPFieldLink fieldLink = new SPFieldLink(field);

Thanks for your help,
NickW
SPSite site = new SPSite(http://TestSite/);

SPWeb web = site.OpenWeb();

web.AllowUnsafeUpdates = true;

//Create new doc library

SPListTemplate listTemplate = web.ListTemplates["Document Library"];

web.Lists.Add(selectedMaster.Reference, "Document Library", listTemplate);

SPList list = web.Lists["TestDocLib"];

list.ContentTypesEnabled = true;

//Create Content Type

SPContentType documentContentType = web.AvailableContentTypes["Document"];

SPContentType newContentType = new SPContentType(documentContentType,
web.ContentTypes, selectedMaster.Reference);


SPField field = new SPField(newContentType.Fields,"Text","Test");

SPFieldLink fieldLink = new SPFieldLink(field);

newContentType.FieldLinks.Add(fieldLink);

newContentType.Update(false);

list.ContentTypes.Add(newContentType);

I am receiving the same error trying to add a field to the newly created document library.

Did you figure out why?

Any clues would be very helpful to me

Thanks

You can think of a SharePoint List somewhat similar to a table present within a Database. As tables consist of different columns, a SharePoint List also comprises of different columns / fields and these fields can indeed have different attributes associated to it (like "Required field check", "Max Length", "Display Formats", etc).
We can use SharePoint API to create these fields and associate the corresponding attributes programmatically within an existing List.

thanks

__________________
Cheers,
Eliza

Often there is a requirement of creating Lists within a SharePoint website programmatically using API calls. Described below are 2 different methods of achieving the same using C#.Net as the programming language.

In the first approach, a SharePoint List gets created using an existing custom List Template present within the List Template Gallery. This approach helps replicate a list exactly in the same structure as of the list from which the custom list template was generated.

In the second approach, a blank SharePoint List gets generated depending on the List Template Type specified during the creation process. This approach can be used to create blank lists of type Announcements, Contacts, Discussion Board, Document Library, Events, Links, Meetings, Picture Library, Survey, Tasks, etc.

Thanks,
Bijayani