Function apply_result_path 

pub fn apply_result_path(
    input: &Value,
    result: &Value,
    path: Option<&str>,
) -> Result<Value, StatesError>

Apply ResultPath to merge a state’s result into the input.

• None or Some("$") -> result replaces input entirely
• Some("null") -> discard result, return original input
• Some("$.foo") -> set result at that path within input

A path that walks into a value that can’t hold its next step ($.a.b with a: 1) fails with States.ReferencePathConflict, as recorded.