The amount_filter object with start_amount and end_amount set to null was always being included in the filter JSON, even when the amount filter wasn't being used. This is inconsistent with other filters (like status, currency, connector) which only appear in the filter JSON when they have actual values.
Added a check to verify if the amount filter is actually being used before creating the amount_filter object. The check validates that at least one of start_amount or end_amount has a non-null value.