code: @SuppressWarnings({"WeakerAccess", "unused"}) // For library users
      public Searcher addNumericRefinement(@NonNull NumericRefinement refinement) {
          SparseArray<NumericRefinement> refinements = numericRefinements.get(refinement.attribute);
          if (refinements == null) {
              refinements = new SparseArray<>();
          }
          refinements.put(refinement.operator, refinement);
          numericRefinements.put(refinement.attribute, refinements);
          rebuildQueryNumericFilters();
          EventBus.getDefault().post(new NumericRefinementEvent(this, ADD, refinement));
          return this;
      }
docs: Adds a numeric refinement for the next queries.
  
  @param refinement a {@link NumericRefinement} refining an attribute with a numerical value.
  @return this {@link Searcher} for chaining.