Function try_build_promoter 

pub fn try_build_promoter<Block, C, P>(
    client: &Arc<C>,
    tx_pool: &Arc<P>,
) -> Option<Arc<dyn HopPromoter>>
where
    Block: BlockT,
    C: HeaderBackend<Block> + ProvideRuntimeApi<Block> + CallApiAt<Block> + Send + Sync + 'static,
    P: LocalTransactionPool<Block = Block> + 'static + ?Sized,

Try to build a HopPromoter by detecting the HopRuntimeApi runtime API at the current best block.

Returns Some(promoter) if the runtime supports the API, or None with a warning log if it doesn’t.