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: _list_fields_output.rs
    path of file: ./repos/aws-sdk-rust/sdk/connectcases/src/operation/list_fields
    
    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.
#[allow(missing_docs)] // documentation missing in model
#[non_exhaustive]
#[derive(::std::clone::Clone, ::std::cmp::PartialEq, ::std::fmt::Debug)]
pub struct ListFieldsOutput {
    /// <p>List of detailed field information.</p>
    pub fields: ::std::vec::Vec<crate::types::FieldSummary>,
    /// <p>The token for the next set of results. This is null if there are no more results to return.</p>
    pub next_token: ::std::option::Option<::std
    
    pub fn build(self) -> ::std::result::Result<crate::operation::list_fields::ListFieldsOutput, ::aws_smithy_types::error::operation::BuildError> {
        ::std::result::Result::Ok(crate::operation::list_fields::ListFieldsOutput {
            fields: self.fields.ok_or_else(|| {
                ::aws_smithy_types::error::operation::BuildError::missing_field(
                    "fields",
                    "fields was not specified but it is required when building ListFieldsOutput",
                )
            })?,
            next_token: self.next_token,
            _request_id: self._request_id,
        })
    }