Arcpy Spatial Join Fails: Field is Not Nullable

We are working to perform a spatial join of a very large point .shp of voters (target_features) with another of incidents (join_features).

arcpy.SpatialJoin_analysis(target_features, join_features, out_features, "JOIN_ONE_TO_MANY")

is working on a small subset of the voters, but when run on the entire set, the error is:

Field is not nullable

for each of the fields in the incidents .shp. Because this is Arc 10.2, we cannot AlterField_management or change the Nullability in Properties as seems possible in 10.3. Instead, we copied the .shp features to a Default.gbd Feature Class (which now claims to have nullable fields in Properties) and re-ran it, but received the same error.

Is there another way to change or ignore the nullability of fields?