A convenience class to encapsulate the logic of variable substitution
based first on any additional variable maps, then flow file properties,
then flow file attributes, and finally the provided variable registry.
Constructs a ValueLookup where values are looked up first based any
provided additional maps, then flowfile properties, then flowfile
attributes, then based on the provided variable registry.
values() - Method in class org.apache.nifi.attribute.expression.language.ValueLookup