presto-main/src/main/java/io/prestosql/operator/scalar/IdentityCast.java/IdentityCast/specialize
class IdentityCast:    @Override
    public ScalarFunctionImplementation specialize(BoundVariables boundVariables, int arity, Metadata metadata)
    {
        checkArgument(boundVariables.getTypeVariables().size() == 1, "Expected only one type");
        Type type = boundVariables.getTypeVariable("T");
        MethodHandle identity = MethodHandles.identity(type.getJavaType());
        return new ScalarFunctionImplementation(
                false,
                ImmutableList.of(valueTypeArgumentProperty(RETURN_NULL_ON_NULL)),
                identity);
    }