Mapping targets will now always be overwritten

In Feeds 7.x-2.0-alpha8 and earlier there was some inconsistency with importing "blank" values (0, NULL or ""). Some mappers ignored empty values, some overwrote the target value.

Mapping targets will now always be overwritten, even if the field does not exists in the source.

Before

Empty values for may be or may not be ignored.

"guid","title","textfield"
1,"Lorem ipsum",""
2,"Ut wisi enim ad minim veniam",0

In Feeds 7.x-2.0-alpha8 and earlier, the textfield would have kept its original value instead of "" or 0.

After

Empty or non-existent values always overwrite the target field.

"guid","title","textfield"
1,"Lorem ipsum",""

An empty string will empty the target textfield.

"guid","title","textfield"
1,"Lorem ipsum",0

An zero will empty the target textfield.

"guid","title"
1,"Lorem ipsum"

A non-existent value will empty the target textfield (if the target is set in the mapping configuration).