code: public @Nonnull ContentMapping getMappingOrCreate(@Nonnull String original, @Nonnull Function<String, ContentMapping> generator) {
          boolean isNew = !mappings.containsKey(original);
          ContentMapping mapping = mappings.computeIfAbsent(original, generator);
          try {
              if (isNew) {
                  save();
              }
          } catch (IOException e) {
              LOGGER.log(Level.WARNING, "Could not save mappings file", e);
          }
          return mapping;
      }
docs: Looks up or creates a new ContentMapping for the given original string and a ContentMapping generator.