Nullness issue - Option.ofObj against non-nullable ref type does not trigger FS3262 when using |>

[isaacabraham]

Issue description

When piping a non-nullable reference type value into Option.ofObj, FS3262 should trigger, but it does not.

Choose one or more from the following categories of impact

• Unexpected nullness warning (false positive in nullness checking, code uses --checknulls and langversion:preview).
• Missing nullness warning in a case which can produce nulls (false negative, code uses --checknulls and langversion:preview).
• Breaking change related to older null constructs in code not using the checknulls switch.
• Breaking change related to generic code and explicit type constraints (null, not null).
• Type inference issue (i.e. code worked without type annotations before, and applying the --checknulls enforces type annotations).
• C#/F# interop issue related to nullness metadata.
• Other (none of the categories above apply).

Operating System

Windows (Default)

What .NET runtime/SDK kind are you seeing the issue on

.NET SDK (.NET Core, .NET 5+)

.NET Runtime/SDK version

.NET 9

Reproducible code snippet and actual behavior

let foo = "test"
let bar = foo |> Option.ofObj // does not produce FS3262

Possible workarounds

Do not use |>

let baz = Option.ofObj foo // fires FS3262

[T-Gro]

FS3262 is not mapped to a "real" language constraint, and it is a bug that it does not flow over the boundary of operator checking.
This will likely be the same case for other compositional operators applied to functions which should warn against "useless null checking".