Allow nullable type for Option fields

[danmt]

Nullable Type for Option Fields

Anchor enables builders to define Optional fields for instruction arguments by using Option in Rust, this works fine, but when using the client in Typescript, the type for the "optional fields" doesn't accept a "nullable" type. i.e. data: Option<u8> in Rust expects data: number in Typescript rather than data?: number or data: number | null.

Expected Behavior

Anchor Typescript client should allow Nullable types for Optional fields.

Solution

The DecodeType from ts/src/program/namespace/type.ts is using conditional types but the option condition defaults to the "option type". If there was a type union for this "option type" with null or undefined, it would work as expected.