Bug report #5172
When a memory layer is "saved as" a shapefile, any null values in the attribute table are converted to zeros
|Affected QGIS version:||master||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||14919|
What the subject says. I don't know if this is really a data provider plugin, or what.
I haven't tested if the same problem occurs saving to shapefile from other formats.
Note that QGIS does support null values in shape files - you can load the resulting file and delete the zeros manually.