UNSUPPORTED_GENERATOR error condition
The generator is not supported:
MULTI_GENERATOR
only one generator allowed per SELECT clause but found <num>: <generators>.
NESTED_IN_EXPRESSIONS
nested in expressions <expression>.
NOT_GENERATOR
<functionName> is expected to be a generator. However, its class is <classCanonicalName>, which is not a generator.
OUTSIDE_SELECT
outside the SELECT clause, found: <plan>.