code: @Nullable
      public static Level getLevelProperty(@Nonnull LogManager manager, @Nonnull String name, @Nullable Level defaultValue) {
          if (name == null) {
              return defaultValue;
          }
          String val = manager.getProperty(name);
          if (val == null) {
              return defaultValue;
          }
          Level l = LevelHelper.findLevel(val.trim());
          return l != null ? l : defaultValue;
      }
docs: Visible version of {@link java.util.logging.LogManager#getLevelProperty(String, java.util.logging.Level)}.
  
  If the property is not defined or cannot be parsed we return the given default value.