Resolve the issue that nonProxyHost was null when toBuilder is called

Author: erin889

http-clients/netty-nio-client/src/main/java/software/amazon/awssdk/http/nio/netty/ProxyConfiguration.java

@@ -271,7 +271,8 @@ private BuilderImpl(ProxyConfiguration proxyConfiguration) {
             this.scheme = proxyConfiguration.scheme;
             this.host = proxyConfiguration.host;
             this.port = proxyConfiguration.port;
-            this.nonProxyHosts = proxyConfiguration.nonProxyHosts;
+            this.nonProxyHosts = proxyConfiguration.nonProxyHosts != null ?
+                                 new HashSet<>(proxyConfiguration.nonProxyHosts) : null;
             this.username = proxyConfiguration.username;
             this.password = proxyConfiguration.password;
         }