Error in (function (classes, fdef, mtable)

I seem to have got rDrop working and have been able to upload files.

However, I am getting the following error related to all commands to either read or list files.

```
> dropbox_acc_info(dropbox_credentials)
Error in (function (classes, fdef, mtable) :
unable to find an inherited method for function ‘fromJSON’ for signature ‘"raw", "missing"’
>
> dropbox_dir(dropbox_credentials, pattern=".rdata")
Error in (function (classes, fdef, mtable) :
unable to find an inherited method for function ‘fromJSON’ for signature ‘"raw", "missing"’
```

Please advise.

Start by reproducing the failure with dropbox_acc_info(dropbox_credentials) and dropbox_dir(dropbox_credentials, pattern=".rdata"). Trace the fromJSON error for the raw, missing signature and compare it with the working upload path; done means the account-info and directory-listing commands read and list files successfully.

Written by the indexing model from the issue text.