"AbstractReadOnlyMap" didn't allow access to the full contents of Maps. It allowed
only access by giving a key. While this makes sense when e.g. querying (big) databases
this broke the "setreplace" function where the whole Map is loaded first to be able
to replace (parts of) the input string.
Allowing access to the entrySet allows the writing of the Set(Entry). To disallow this
the map used in FileMap is made into an "unmodifiable Map".
"AbstractReadOnlyMap" didn't allow access to the full contents of Maps. It allowed only access by giving a key. While this makes sense when e.g. querying (big) databases this broke the "setreplace" function where the whole Map is loaded first to be able to replace (parts of) the input string. Allowing access to the entrySet allows the writing of the Set(Entry). To disallow this the map used in FileMap is made into an "unmodifiable Map".