code: @SuppressWarnings({"WeakerAccess", "unused"}) // For library users
      public Searcher addBooleanFilter(String attribute, Boolean value) {
          booleanFilterMap.put(attribute, value);
          rebuildQueryFacetFilters();
          return this;
      }
docs: Adds a boolean refinement for the next queries.
  
  @param attribute the attribute to refine on.
  @param value     the value to refine with.
  @return this {@link Searcher} for chaining.