chore: warning when proxy property is undefined

Author: evenstensberg

lib/Server.js

@@ -832,6 +832,9 @@ class Server {
       if (proxyConfig.target) {
         return createProxyMiddleware(context, proxyConfig);
       }
+      this.logger.warn(
+        `The "target" value specified in the "proxy" property ${context} is not defined and will be skipped.`
+      );
     };
     /**
      * Assume a proxy configuration specified as: