docs: public static GrammaticalRelation getPrep(String prepositionString) {
      GrammaticalRelation result = preps.get(prepositionString);
      if (result == null) {
        synchronized(preps) {
          result = preps.get(prepositionString);
          if (result == null) {
            result = new GrammaticalRelation(Language.English, "prep", "prep_collapsed", null, PREPOSITIONAL_MODIFIER, prepositionString);
            preps.put(prepositionString, result);
            threadSafeAddRelation(result);
          }
        }
      }
      return result;
    }