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: _export_tr31_key_block.rs
    path of file: ./repos/aws-sdk-rust/sdk/paymentcryptography/src/types
    
    the code of the file until where you have to start completion: // Code generated by software.amazon.smithy.rust.codegen.smithy-rs. DO NOT EDIT.

/// <p>Parameter information for key material export using symmetric TR-31 key exchange method.</p>
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq, ::std::fmt::Debug)]
pub struct ExportTr31KeyBlock {
    /// <p>The <code>KeyARN</code> of the the wrapping key. This key encrypts or wraps the key under export 
    
    pub fn build(self) -> ::std::result::Result<crate::types::ExportTr31KeyBlock, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::ExportTr31KeyBlock {
            wrapping_key_identifier: self.wrapping_key_identifier.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "wrapping_key_identifier",
                    "wrapping_key_identifier was not specified but it is required when building ExportTr31KeyBlock",
                )
            })?,
        })
    }