OfflineContentManager export_items fails for "Tile layer (hosted)" map service

[knoopum]

Describe the bug
When using the OfflineContentManager's export_items method with a "Tile layer (hosted)" map service, published from a Tile Package, it unexpectedly fails. (See error message below.)

To Reproduce
In order to reproduce the issue you can attempt to use export_items with a "Tile layer (hosted)" map service, published from a Tile package. It will result in the following error:

C:\Users\knoop\AppData\Local\ESRI\conda\envs\work\Lib\site-packages\arcgis\apps\itemgraph\_migration.py:149: RuntimeWarning: Failed to export item 9ad056d339534fdb9c75fa354491f101 due to error: <MapRasterLayer url:"https://tiles.arcgis.com/tiles/4ezfu5dIwH83BUNL/arcgis/rest/services/Environs_Jerusalem_NLI/MapServer/0"> is not JSON serializable. Deleting folder and skipping...
  warnings.warn(

Expected behavior
I expect export_items to be able to successfully export a "Tile layer (hosted)" map service, including its Tile package.

Platform (please complete the following information):
Python API 2.4.2

[achapkowski]

Is this enterprise or ArcGIS Online?
Please provide a code snippet as text, no screenshots.

[knoopum]

@achapkowski The error occurs with a Tile layer (hosted) on ArcGIS Online.

The example Tile layer (hosted) in the snippet below is shared publicly, but owned by a different user than the admin user running the code.

import arcgis
from arcgis import GIS
import os
import pandas

# Connect to ArcGIS Online organization as an admin user
gis = GIS(profile="xxxxxxxx")  

# Items to backup -- publicly shared Tile layer (hosted), published from Tile package
items = [
    gis.content.get('9ad056d339534fdb9c75fa354491f101')
]
display(pandas.DataFrame(items, columns=["id","type","typeKeywords","title"]))

# Export offline backup package
package_path = gis.content.offline.export_items(
    items = items,
    output_folder = os.getcwd(),
    package_name = "ocm_tile_layer_hosted",
)
print(package_path)