Describes that an error happened in user-written subclass code or options.
This exception is never purposefully thrown by the core LazyJsonMapper
class by default. It's only thrown if problems happen in subclass code or
if there are problems related to the user-class options.
Currently, that's only possible in the LazyJsonMapper::_init() function,
or when the user has overridden certain user-class options away from
the default values and then attempts to perform an action affected by
their non-standard class option.