code: public void purge(@NonNull Document document) throws CouchbaseLiteException {
          if (document == null) { throw new IllegalArgumentException("document cannot be null."); }
  
          if (document.isNewDocument()) {
              throw new CouchbaseLiteException("Document doesn't exist in the database.",
                  CBLError.Domain.CBLITE, CBLError.Code.NOT_FOUND);
          }
  
          synchronized (lock) {
              prepareDocument(document);
  
              boolean commit = false;
              beginTransaction();
              try {
                  // revID: null, all revisions are purged.
                  if (document.getC4doc().purgeRevision(null) >= 0) {
                      document.getC4doc().save(0);
                      // Reset c4doc:
                      document.replaceC4Document(null);
                      commit = true;
                  }
              }
              catch (LiteCoreException e) {
                  throw CBLStatus.convertException(e);
              }
              finally {
                  endTransaction(commit);
              }
          }
      }
docs: Purges the given document from the database. This is more drastic than delete(Document),
  it removes all traces of the document. The purge will NOT be replicated to other databases.
  
  @param document