Creates a new RangeError stating that index is not a valid index
into indexable.
An optional name can specify the argument name that has the
invalid value, and the message can override the default error
description.
The length is the length of indexable at the time of the error.
If length is omitted, it defaults to indexable.length.
Source
factory RangeError.index(int index, indexable,
[String name, String message, int length]) = IndexError;