public string Serialize()
{
if (RelType == RelationshipType.Custom && string.IsNullOrWhiteSpace(CustomRelType))
{
throw new ArgumentException("Invalid custom relationship type! Type needs to be custom as well when custom type name is explicitly set!");
}
return($"RELTYPE={ (RelType == RelationshipType.Custom ? CustomRelType : RelType.ToString().ToUpper()) }");
}
