DevOps migration tool: ArgumentNullException: Value cannot be null - azure-devops-migration-tools

Question

I'm trying to migrate tickets from one org/project to an other org/project, but not with success at the moment.
I have tried to config it the correct way, but I guees I have filled it in correctly now (see below) and still I get the following error.
note: it looks like the 'Source Node Path StartsWith' in the log is not correct. We do not use (sub) Area's. Area should be: vdp-bam-gen.
I tried to leave out the LanguageMaps and also empty the value (AreaPath": ""). But I still get (other) errors.
NodeStructureEnricher.ProcessCommonStructure(Area, Area)
-Source Node Path StartsWith [\vdp-bam-gen\area]
Error while running WorkItemMigration
System.ArgumentNullException: Value cannot be null.
Parameter name: source
at System.Linq.Enumerable.Where[TSource](IEnumerable1 source, Func2 predicate)
I cannot copy my whole config, but here are some parts:
Version": "12.0",
"TelemetryEnableTrace": false,
"workaroundForQuerySOAPBugEnabled": false,
"Source": {
"$type": "TfsTeamProjectConfig",
"Collection": "https://a_url_of my project/",
"Project": "VDP-BAM-GEN",
"ReflectedWorkItemIDFieldName": "Custom.ReflectedWorkItemId",
"AllowCrossProjectLinking": false,
"AuthenticationMode": "Prompt",
"LanguageMaps": {
"AreaPath": "Area",
"IterationPath": "Iteration"
}
"Target": {
"$type": "TfsTeamProjectConfig",
"Collection": "https://a_url_of my project/",
"Project": "CIT-BAM-SOURCING-CUSTOMERS",
"ReflectedWorkItemIDFieldName": "Custom.ReflectedWorkItemId",
"AllowCrossProjectLinking": false,
"AuthenticationMode": "Prompt",
"LanguageMaps": {
"AreaPath": "Area",
"IterationPath": "Iteration"
"Processors": [
"$type": "WorkItemDeleteConfig",
"Enabled": true,
"QueryBit": "AND [System.WorkItemType] NOT IN ('Test Suite', 'Test Plan', 'Epic', 'Feature', 'User Story','Bug','Inbox Item')",
"OrderBit": "[System.ChangedDate] desc"
,
"$type": "WorkItemMigrationConfig",
"ReplayRevisions": true,
"PrefixProjectToNodes": false,
"UpdateCreatedDate": false,
"UpdateCreatedBy": false,
"BuildFieldTable": false,
"AppendMigrationToolSignatureFooter": false,
"QueryBit": "AND [System.WorkItemType] NOT IN ('Test Suite', 'Test Plan', 'Epic', 'Feature', 'User Story','Bug','Inbox Item')",
"OrderBit": "[System.ChangedDate] desc",
"Enabled": true,
"LinkMigration": true,
"AttachmentMigration": true,
"AttachmentWorkingPath": "c:\tmp\WorkItemAttachmentWorkingFolder",
"FixHtmlAttachmentLinks": false,
"SkipToFinalRevisedWorkItemType": false,
"WorkItemCreateRetryLimit": 5,
"FilterWorkItemsThatAlreadyExistInTarget": true,
"PauseAfterEachWorkItem": false,
"AttachmentMaxSize": 480000000,
"CollapseRevisions": false,
"LinkMigrationSaveEachAsAdded": false