Updating the Sensitive Properties Key
Starting with version 1.14.0, NiFi requires a value for 'nifi.sensitive.props.key' in nifi.properties.
The following command can be used to read an existing flow.xml.gz configuration and set a new sensitive properties key in nifi.properties:
$ ./bin/nifi.sh set-sensitive-properties-key <sensitivePropertiesKey>
The minimum required length for a new sensitive properties key is 12 characters.