getTile method
Retrieve a tile from the cache, if it exists
Returns null if the tile was not present in the cache.
If the tile was present, but could not be correctly read (for example, due
to an unexpected corruption), this may throw CachedMapTileReadFailure.
Additionally, any returned tile image bytes are not guaranteed to form a
valid image - attempting to decode the bytes may also throw.
Tile providers should anticipate these exceptions and fallback to a
non-caching alternative, wherever possible repairing or replacing the tile
with a fresh & valid one.
Implementation
@override
Never getTile(String url) =>
throw UnsupportedError('Must not be called if `isSupported` is `false`');