Raise error/give warning when global PedAttributes and source-specific PedAttributes co-exist

Problem to solve

If source-specific PedestrianAttributes exist for a special source (default: null), the global attributes are overwritten for this special source. If there are multiple sources in the scenario with some of them overwriting attributes and some of them NOT overwriting attributes, it can be confusing.

Goal

if only global PedestrianAttributes are defined => ok
if only source-specific PedestrianAttributes are defined => ok
if both is defined at the same time => warn the user or throw an exception

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