code: public boolean save(@NonNull MutableDocument document, @NonNull ConcurrencyControl concurrencyControl)
          throws CouchbaseLiteException {
          if (document == null) { throw new IllegalArgumentException("document cannot be null."); }
          if (concurrencyControl == null) { throw new IllegalArgumentException("concurrencyControl cannot be null."); }
  
          // NOTE: synchronized in save(Document, boolean) method
          return save(document, false, concurrencyControl);
      }
docs: Saves a document to the database. When used with LAST_WRITE_WINS
  concurrency control, the last write operation will win if there is a conflict.
  When used with FAIL_ON_CONFLICT concurrency control, save will fail with false value
  
  @param document           The document.
  @param concurrencyControl The concurrency control.
  @return true if successful. false if the FAIL_ON_CONFLICT concurrency
  @throws CouchbaseLiteException