[provide a description of the issue]
acoording to https://microsoft.github.io/debug-adapter-protocol/specification

`A client or debug adapter initiated request.

interface Request extends ProtocolMessage {
type: 'request';

/**

• The command to execute.
  */
  command: string;

/**

• Object containing arguments for the command.
  */
  arguments?: any;
  }
  `
  When argument isn't exist . It's an JsonNull bject .
  When JsonNull exist. it's an JsonObject boject.

So The filed which named arguments of com.microsoft.java.debug.core.protocol.Messages.Request class shoulb be JsonElement type .