question: public static CommitVersionInfo build ( IndexCommit commit ) { long generation = commit . getGeneration ( ) ; long version = 0 ; try { final Map < String , String > commitData = commit . getUserData ( ) ; String commitTime = commitData . get ( SolrIndexWriter . COMMIT_TIME_MSEC_KEY ) ; if ( commitTime != null ) { try { version = Long . parseLong ( commitTime ) ; } catch ( NumberFormatException e ) { LOG . warn ( "Version in commitData was not formated correctly: " + commitTime , e ) ; } } } catch ( IOException e ) { LOG . warn ( "Unable to get version from commitData, commit: " + commit , e ) ; } return new CommitVersionInfo ( generation , version ) ; }
target:  builds a CommitVersionInfo data for the specified IndexCommit.   Will never be null, ut version and generation may be zero if  there are problems extracting them from the commit data