Problem when adding an existing site field to a content type

[dgtheninja]

Category

• Bug

When adding an existing site field to a content type following the instructions from https://pnp.github.io/pnpcore/using-the-sdk/contenttypes-intro.html#adding-site-fields-to-a-site-content-type
awaitcontentType.FieldLinks.AddAsync(field, required: true);

if you don't specify a Display Name then when you try and add the content type to a list, either programmatically or through the UI, you get an error like
Can not add a field without a Display Name.

Steps to reproduce

var ct = await context.Web.ContentTypes.AddAsync("<CT ID>", "<CT Name>", group: "Test");
var field = await context.Web.Fields.FirstOrDefaultAsync(f => f.InternalName == "<Field Name>");
await ct.FieldLinks.AddAsync(field);

Expected behavior

On the above AddAsync method if the optional displayName parameter is not passed then should it copy the Title from the field property? I presume the optional parameters are there to override the values from the field (I have not tested this behaviour)?

Note, workaround is to pass the display name

await ct.FieldLinks.AddAsync(field, displayName: field.Title);

Environment details (development & target environment)

• SDK version: 1.5.85-nightly
• OS: Windows Server 2022
• SDK used in: Azure Functions
• Framework: .NET 6
• Browser(s): n/a
• Tooling: Visual Studio 2022

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[jansenbe]

Nice catch @dgtheninja , by default the code tried to set the fieldlink displayname while the default value for that one was set to null. I'll add a check to avoid the problem.

[jansenbe]

Closing this one now that fix is in.

[dgtheninja]

Brilliant, thanks @jansenbe