为什么在Option :: unwrap（）中创建Reqwest客户端恐慌？

extern crate reqwest;

fn main() {
    let client = reqwest::Client::new();
}

当我运行这个时，我得到了这个错误 .

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', libcore/option.rs:345:21

我也尝试了它与构建器，但错误仍然相同 .

extern crate reqwest;

fn main() {
    let mut client = reqwest::Client::builder(); // Panics here 
    match client.build() {
        Err(e) => {println!("{:?}", e);}
        _ => {}
    }
}

这里是这段代码的完整堆栈回溯 .

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', libcore/option.rs:345:21
    stack backtrace:
       0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:511
   5: std::panicking::continue_panic_fmt
             at libstd/panicking.rs:426
   6: rust_begin_unwind
             at libstd/panicking.rs:337
   7: core::panicking::panic_fmt
             at libcore/panicking.rs:92
   8: core::panicking::panic
             at libcore/panicking.rs:53
   9: <core::option::Option<T>>::unwrap
             at /checkout/src/libcore/macros.rs:20
  10: openssl::ssl::SslContextBuilder::set_options
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/openssl-0.9.24/src/ssl/mod.rs:905
  11: openssl::ssl::connector::ctx
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/openssl-0.9.24/src/ssl/connector.rs:42
  12: openssl::ssl::connector::SslConnectorBuilder::new
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/openssl-0.9.24/src/ssl/connector.rs:67
  13: native_tls::imp::TlsConnector::builder
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/native-tls-0.1.5/src/imp/openssl.rs:186
  14: native_tls::TlsConnector::builder
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/native-tls-0.1.5/src/lib.rs:390
  15: reqwest::async_impl::client::ClientBuilder::new
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/reqwest-0.8.6/src/async_impl/client.rs:79
  16: reqwest::client::ClientBuilder::new
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/reqwest-0.8.6/src/client.rs:63
  17: reqwest::client::Client::builder
             at /home/ubuntu/.cargo/registry/src/github.com-1ecc6299db9ec823/reqwest-0.8.6/src/client.rs:281
  18: project::proj::tp_app::uploader::start
             at src/proj/tp_app/uploader.rs:4