Enhance error message on a very basic usage

[pawelru]

> rtables::rtable(1)
Error in rtables::rtable(1) : problems
> packageVersion("rtables")
[1] ‘0.4.0.2.1’

Please elaborate more what kind of problem has been detected or indicate that you are expecting certain class of argument

[gmbecker]

Hi @pawelru,

Can you tell me what you would expect rtables(1) to produce as a user? There is either no header information out of which we can make the columns, or there are no rows.

[pawelru]

I want the error message exactly as you said: this and this is missing - not the error message is very cryptic

[gmbecker]

HI Pawel,

Again, I Was not asking what you thought the error should say, I will change the error message. What I would like to know, however, is what the user thought the table that came out of that call would be. That will help improving the documentation so that no one ever makes a call like that in the first place (which they should not).

[pawelru]

What I would like to know, however, is what the user thought the table that came out of that call would be.

That's only my experiments with rtables API. And there I am not expecting any table out of it - just a meaningful error message saying what arguments are required.