(node_pks: &[PublicKey], keys_manager: &K, secp_ctx: &Secp256k1<T>) -> Result<Self, ()>
{
if node_pks.len() < 2 { return Err(()) }
(node_pks: &[PublicKey], keys_manager: &K, secp_ctx: &Secp256k1<T>) -> Result<Self, ()>
{
if node_pks.len() < 2 { return Err(()) }