IgnoreRespectNulls returns as List and should be a different type

We would expect a proper Fragment class IgnoreRespectNullsClause or maybe a simple a simple enum

Maybe something along the following lines?

public enum IgnoreRespectNulls
{
NotSpecified,
IgnoreNulls,
RespectNulls
}

Start by locating the API member that exposes IgnoreRespectNulls and checking its callers and tests. Compare the existing List return type with the proposed IgnoreRespectNullsClause or enum, then determine the compatible public API change. Done means the return type represents the three stated states and affected tests or consumers pass.

Written by the indexing model from the issue text.