If you have noticed below log line of ERROR in your SDC or data collector logs, it is possible that the `time:extractStringFromDateTZ` function having a null date object after the evaluation of its first parameter.
Invalid parameter - Date is null TimeNowELSolution: This is expected since time:extractStringFromDateTZ function is unaware of what is being evaluated in its parameter. If you are using something like `record:value*` to retrieve the date object and if it happens to be null, the above error is logged.
`Returns an empty string when the time zone is not specified or invalid` is mentioned in doc that it needs to be expected.
In case if you would like to filter out or categorize the record(s) containing field(s) of null as error, please consider using a stream selector stage to move such records to To Error stage.