The `exampleMap` needs to hold an hash object for each
of the `collectExamples.exampleFolders` paths.
Previously these hash objects were only created if there
was actually an example file the hash's respective
example folder. This could cause crashes during
`yarn docs-watch` (and so also `yarn sync-and-serve`)
if no examples were read in for a particular run of
the doc-gen.
PR Close#22502
Pete Bacon Darwin