pub fn to_block(mut self, block: BlockNumber) -> Self {
        self.filter.block_hash = None;
        self.filter.to_block = Some(block);
        self
    }
Sets `to_block`. The fields `to_block` and `block_hash` are mutually
exclusive. Setting `to_block` will clear a previously set `block_hash`.
core/lib/basic_types/src/web3/mod.rs