question: @ VisibleForTesting protected Set < String > calculateDeletedServerDefaults ( Map < String , String > existingDefaults , Map < String , String > validServerProperties ) { Set < String > deletedValues = new HashSet < String > ( ) ; for ( String existingAttr : existingDefaults . keySet ( ) ) { int startBracket = existingAttr . indexOf ( '[' ) ; if ( startBracket != - 1 ) { existingAttr = existingAttr . substring ( 0 , startBracket ) ; } if ( ! validServerProperties . containsKey ( existingAttr ) ) { deletedValues . add ( existingAttr ) ; } } return deletedValues ; }
target:  Finds deleted attributes by comparing the currently defined properties against the new valid server properties. By comparing against the valid server properties we can ensure that manually defined custom properties will not be removed.