presto-main/src/main/java/io/prestosql/operator/ParametricImplementationsGroup.java/Builder/build
class Builder:        public ParametricImplementationsGroup<T> build()
        {
            Map<Signature, T> exactImplementations = this.exactImplementations.build();
            List<T> specializedImplementations = this.specializedImplementations.build();
            List<T> genericImplementations = this.genericImplementations.build();
            return new ParametricImplementationsGroup<>(
                    exactImplementations,
                    specializedImplementations,
                    genericImplementations,
                    determineGenericSignature(exactImplementations, specializedImplementations, genericImplementations));
        }