message: [lang] Add check for empty parameters for messages
diff: @@ -122,17 +122,24 @@ impl Contract {
  }
  let inputs = &msg.sig.decl.inputs;
  {
  - let self_ty: &ast::FnArg = inputs.first().unwrap().into_value();
  - match self_ty {
  + match inputs.first().map(|arg| arg.into_value()) {
  + None => {
  + bail!(
  + msg.sig.ident,
  + "contract messages must operate on `&self` or `&mut self`"
  + )
  + }
  + Some(self_ty) => match self_ty {
  ast::FnArg::SelfValue(_) | ast::FnArg::Captured(_) => {
  bail!(
  self_ty,
  - "contract messages must start with `&self` or `&mut self`"
  + "contract messages must operate on `&self` or `&mut self`"
  )
  }
  _ => (),
  }
  }
  + }
  for fn_arg in inputs.iter().skip(1) {
  if let ast::FnArg::Captured(arg_captured) = fn_arg {
  if let syn::Pat::Ident(pat_ident) = &arg_captured.pat {
  