This annotation is to be used on a Groovy method which
is part of an Accumulator UDF to indicate that it will
act as the 'accumulate' method of the UDF.
The value of the annotation is the name of the Accumulator UDF
it belongs to.
The annotated method MUST NOT be static and MUST accept a single groovy.lang.Tuple as parameter.
Its return value, if any, is ignored.