Error when original guid does not exist in the source file for mapped reference field

[ksulikow]

Describe the bug
When export config contains fields mappings defined, but has the reference field excluded from export, the original guid will not be included in the exported data. It will cause error and fail during import.

To Reproduce
Create export config file and configure lookup mapping and add the field to excluded fields
"ExcludedFields": [
"systemuserid",
"roleid",
"systemuserrolesid",
"businessunitid"
],
"LookupMapping": {
"systemuser": {
"systemuserid": [
"domainname"
],
"businessunitid": [
"name"
]
},
"systemuserroles": {
"systemuserid": [
"domainname"
],
"roleid": [
"name",
"businessunitid"
]
}
}

Expected behavior
In this situation if lookup value can be found in the target system then it should be used, if not it should be left empty

Additional context
Fatal error during import