message: Report an error on wrong parameter
diff: // Copyright (c) SimpleStaking and Tezedge Contributors
  // SPDX-License-Identifier: MIT
  +use failure::format_err;
  use hyper::{Body, Request};
  use slog::warn;
  @@ -119,7 +120,9 @@ pub async fn dev_action_cursor(
  env.persistent_storage(),
  )
  } else {
  - unreachable!()
  + Err(format_err!(
  + "Invalid parameter: should be either `block_hash` or `contract_address`"
  + ))
  },
  env.log(),
  )
  