dbg!() without parameters

[inv2004]

Hello,
I found dbg!(..) is very useful, but, unfortunately it does not support dbg!() without expression, which could help to debug your program also.

I found that println!() did not work in first versions also, but later it was fixed, that is why I suppose dbg!() has the same story.

dbg!(()) is ok, but its just workaround.

Thank you,

[mark-i-m]

Could you make a PR for this?

[clarfonthey]

I just made a PR for this.