Function yyjson_mut_arr_add_null 

pub unsafe extern "C" fn yyjson_mut_arr_add_null(
    doc: *mut yyjson_mut_doc,
    arr: *mut yyjson_mut_val,
) -> bool

Adds a null value at the end of the array. @param doc The doc is only used for memory allocation. @param arr The array to which the value is to be inserted. Returns false if it is NULL or not an array. @return Whether successful.