`INV` allows `INT` and `FLT` arg.

[python-processing-unit]

According to the specification section 9.1.7:

• MAP: INV(MAP: map) = MUST return a new map whose keys and values are reversed. Every value in map MUST be a scalar key type (INT, FLT, or STR), and duplicate values MUST raise a runtime error.

In the implementation, however, INV does not error on an INT or FLT arg.