Correct me if wrong.
The statement should be problematic since it is grammatically wrong.
But it can still be seen in several occasions:
- the heading in a newspaper (reason: to save space)
- in a song (reason: rhyme, musical, pleasant to eye etc.)
- conversation (reason: people are lazy

)
I think the person who said it was an idiom use this word loosely. They might wish to say it is just a casual statement like "long time no see". Grammatically incoorect for sure. Still acceptable in some sitautions.