Cryptic error message in join when `y` is `NULL`

[DanChaltiel]

Hi,

This error message is not very informative:

dplyr::left_join(iris, NULL, by=Species)
#> Error in `auto_copy()`:
#> ! `x` and `y` must share the same src.
#> i set `copy` = TRUE (may be slow).
#> Backtrace:
#>     x
#>  1. +-dplyr::left_join(iris, NULL, by = Species)
#>  2. \-dplyr:::left_join.data.frame(iris, NULL, by = Species)
#>  3.   \-dplyr::auto_copy(x, y, copy = copy)
#>  4.     \-rlang::abort(bullets)

^{Created on 2023-03-21 with reprex v2.0.2}

Wouldn't it be better to simply tell us the second dataframe was unexpectedly NULL?

Experienced with dplyr v1.1.0, sorry I cannot test with the dev version right now.