Adding Null Parameters for Export

Adding null parameters for export
Null Parameters for export were not not included in the current version
"input.null.non-string" and "input.null.string".
Rather than set a default value on the data, wouldn't it be better to force the user to provide the null string when they try to export through the Sqoop API in Maestro. We have issue https://github.com/CommBank/maestro/issues/201 to do this for import. Making a conscience choice about nulls in data is important in my opinion.