How to declare collection of non-nullable references?

[sherlock1982]

I use conventional builder to make my model.
Somewhere I have this definition:

    [DataMember]
    public string[]? Codecs { get; set; }

And in metadata it looks like this:

<Property Name="Codecs" Type="Collection(Edm.String)"/>

Which is from my understanding a nullable collection of nullable strings.
I do understand that from a code point of view string is a nullable reference type.
But is there a way to declare that this specific collection contains non-nullable strings?

[corranrogue9]

I think there are two parts of the question: nullable collection and nullable elements.

nullable collections

The standard says:

For collection-valued properties the property value will always be a collection that MAY be empty. In this case the Nullable attribute applies to items of the collection and specifies whether the collection MAY contain null values.

If no value is specified for a single-valued property, the Nullable attribute defaults to true.

The implication of this is that, in OData, there is no such thing as a "nullable collection". Collection properties, when present, will always have a value (though they may be empty); they will never be "Codec": null.

nullable elements

I have created a repro of this here and it executes exactly as you say. Note from the snippet of the standard above that this CSDL is actually a collection of nullable strings since when Nullable is not specified in the CSDL, the default value is that the elements are nullable. My suggestion to you is to simply remove the ? from your property and you have as close to what you desire as OData allows.

[corranrogue9]

I think we should create a separate issue to track this since it's unrelated to your question @sherlock1982, but the second test I wrote demonstrates that the non-nullable case doesn't seem to be supported. We will discuss this in triage.

[sherlock1982]

I see what you mean, thanks for the answer!
Though I don't fully understand as if I remove ? C# will ask me to initialize the collection which is completely ok. But when I for example make a PATCH request and do not specify the collection will it mean that I will actually receive empty collection in the Delta or instance?

Because empty collection and absence of a collection are different things