These are popping up in my garden this year.
I did some online research,
Our American Nightshade is Solanum americanum, not nigrum.
Good 'ole Wikipedia has a great article on it https://en.wikipedia.org/wiki/Solanum_americanum
German Wiki has a great article on S. nigrum and tries to pinpoint the cause of S.n and S. a's dual nature.
Translated from the German wiki page on Solanum nigrum: Due to the high content of alkaloids , especially in the immature berries, the plant is often categorized as a poisonous plant, but ripe berries and the leaves are used as vegetables in some parts of the world. Include all parts of the black nightshade which the glyco alkaloids attributed to steroid alkaloids solanine , Solasonine , solamargine and chaconine, The concentration of these substances varies very strongly and is probably dependent on the climate
and type of soil
in which the plant grows, in addition the concentration decreases with increasing age of the plant
. This explains why there are numerous evidence that either categorize the plant as a poisonous plant or describe it as a foodstuff. In fresh leaves, 1 mg / 100 g of ascorbic acid
(vitamin C) was detected. 
There is a book about Nightshades I found FREE online. https://books.google.com/books?id=nfau8bsLyUUC&lpg=PA5&ots=KirxF8-AYT&dq=solanum+nigrum+medicinal+uses&lr=&pg=PP1&hl=en#v=onepage&q=solanum%20nigrum%20medicinal%20uses&f=false
The USDA site:https://plants.usda.gov/core/profile?symbol=SOAM
In German, the name translates into Black Night Shadows which sounds very poetic.
I hope this helps!