pub fn block_hash(mut self, hash: H256) -> Self {
        self.filter.from_block = None;
        self.filter.to_block = None;
        self.filter.block_hash = Some(hash);
        self
    }
Sets `block_hash`. The field `block_hash` and the pair `from_block` and
`to_block` are mutually exclusive. Setting `block_hash` will clear a
previously set `from_block` and `to_block`.
core/lib/basic_types/src/web3/mod.rs