presto-main/src/main/java/io/prestosql/operator/scalar/MapElementAtFunction.java/MapElementAtFunction/MapElementAtFunction
class MapElementAtFunction:    protected MapElementAtFunction()
    {
        super(new FunctionMetadata(
                new Signature(
                        "element_at",
                        ImmutableList.of(typeVariable("K"), typeVariable("V")),
                        ImmutableList.of(),
                        new TypeSignature("V"),
                        ImmutableList.of(mapType(new TypeSignature("K"), new TypeSignature("V")), new TypeSignature("K")),
                        false),
                true,
                ImmutableList.of(
                        new FunctionArgumentDefinition(false),
                        new FunctionArgumentDefinition(false)),
                false,
                true,
                "Get value for the given key, or null if it does not exist",
                SCALAR));
    }