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: _tag.rs
    path of file: ./repos/aws-sdk-rust/sdk/iot/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>A set of key/value pairs that are used to manage the resource.</p>
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq, ::std::fmt::Debug)]
pub struct Tag {
    /// <p>The tag's key.</p>
    pub key: ::std::string::String,
    /// <p>The tag's value.</p>
  
    
    pub fn build(self) -> ::std::result::Result<crate::types::Tag, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::Tag {
            key: self.key.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field("key", "key was not specified but it is required when building Tag")
            })?,
            value: self.value,
        })
    }