XWIKI-19770: NPE when inserting some macros

...iki-platform-mentions/xwiki-platform-mentions-api/pom.xml

...ns-api/src/main/java/org/xwiki/mentions/DisplayStyle.java

...pi/src/test/java/org/xwiki/mentions/DisplayStyleTest.java

...platform-mentions/xwiki-platform-mentions-default/pom.xml

...s/internal/analyzer/AbstractDocumentMentionsAnalyzer.java

...entions/internal/rendering/PlainTextMentionsRenderer.java

...ternal/analyzer/AbstractDocumentMentionsAnalyzerTest.java