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: _custom_parameter.rs
    path of file: ./repos/aws-sdk-rust/sdk/datazone/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>The details of user parameters of an environment blueprint.</p>
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq)]
pub struct CustomParameter {
    /// <p>The key name of the parameter.</p>
    pub key_name: ::std::string::String,
    /// <p>The description of the parameter.</p>
    pub description: ::std::option::Option<::std::string::String>,
    /// <p>The filed t
    
    pub fn build(self) -> ::std::result::Result<crate::types::CustomParameter, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::types::CustomParameter {
            key_name: self.key_name.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "key_name",
                    "key_name was not specified but it is required when building CustomParameter",
                )
            })?,
            description: self.description,
            field_type: self.field_type.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "field_type",
                    "field_type was not specified but it is required when building CustomParameter",
                )
            })?,
            default_value: self.default_value,
            is_editable: self.is_editable,
            is_optional: self.is_optional,
        })
    }