presto-main/src/main/java/io/prestosql/operator/scalar/MapConcatFunction.java/MapConcatFunction/MapConcatFunction
class MapConcatFunction:    private MapConcatFunction()
    {
        super(new FunctionMetadata(
                new Signature(
                        FUNCTION_NAME,
                        ImmutableList.of(typeVariable("K"), typeVariable("V")),
                        ImmutableList.of(),
                        mapType(new TypeSignature("K"), new TypeSignature("V")),
                        ImmutableList.of(mapType(new TypeSignature("K"), new TypeSignature("V"))),
                        true),
                false,
                ImmutableList.of(new FunctionArgumentDefinition(false)),
                false,
                true,
                DESCRIPTION,
                SCALAR));
    }