3567884: Fixed PHP warnings: Undefined property rdfs:label and rdfs:comment in...

Anna Demianikrequested to merge
issue/json_ld_schema_ui-3567884:3567884-php-warnings-undefined into 1.0.x

3567884: Fixed PHP warnings: Undefined property rdfs:label and rdfs:comment in GraphNodeBase::fromElement()

Closes #3567884

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