When Creating a new Schema it is possible to directly change all of the settings of an imported field (Field Name, Field Type, Field Alias, Default Value, Domain, Length, Precision, Scale) except for the Allow NULL Values property. Clicking on that property after importing a schema does not trigger the normal combobox behavior that lets a user choose to enable or disable that property.
There are only two ways to change the Allow NULL Values property. The first is to change the field type to a different type. However, by changing the field type other field properties are reset. After changing back to the original type just to alter the Allow NULL Values property, user error can easily occur in the process of trying to remember and restore the other properties to what was originally imported.
Most people (including myself prior to this post) will not realize that changing the type can enable the Allow NULL Values property. They will normally delete that field and recreate it, which may cause even more user error when restoring all of the settings just to change the Allow Null Value property. This just happened to me on a complex feature class I spent hours rebuilding and I am ticked.
