You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/namada/crates/apps/src/lib/node/ledger/shell
    
    the code of the file until where you have to start completion: //! The ledger shell connects the ABCI++ interface with the Namada ledger app.
//!
//! Any changes applied before [`Shell::finalize_block`] might have to be
//! reverted, so any changes applied in the methods [`Shell::prepare_proposal`]
//! and [`Shell::p
    
    pub fn get_protocol_key(&self) -> Option<&common::SecretKey> {
        match self {
            ShellMode::Validator {
                data:
                    ValidatorData {
                        keys:
                            ValidatorKeys {
                                protocol_keypair, ..
                            },
                        ..
                    },
                ..
            } => Some(protocol_keypair),
            _ => None,
        }
    }