code: public T get() {
          return getInternal(
                  x -> x,
                  () -> {
                      T defaultValue = defaultExpression.get();
                      if (defaultValue == null) {
                          throw new IllegalStateException("Value is not set: " + name);
                      }
                      value = defaultValue;
                      return defaultValue;
                  }
          );
      }
docs: Returns the value of this setting. If the values was not set, it is set to the (lazily evaluated) default value
  first. If the expression that calculates the default value returns null, an <code>IllegalStateException</code>
  is thrown.
  @return The value of this setting
  @throws java.lang.IllegalStateException When the value is not set