Github user ottobackwards commented on the issue:
https://github.com/apache/nifi/pull/2777
Maybe there should be a `Context` interface, and there can be support for
implementations that support more than one map or type of backing. I think the
limitation here is using a literal Map instead of a logical construct.
This is similar to variable resolution in a custom language. You may need
more than a map.
`LookupContext context = new AttributeAndCoordinateLookup(attrs, coords);`
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