Ensure the router is approved to spend amountIn of the input token, sending an approve transaction only when the current allowance is short. Returns the approval tx hash, or null when no approval was needed.
amountIn
approve
null
Ensure the router is approved to spend
amountInof the input token, sending anapprovetransaction only when the current allowance is short. Returns the approval tx hash, ornullwhen no approval was needed.