code: public <T> ServerBootstrap childAttr(AttributeKey<T> childKey, T value) {
          if (childKey == null) {
              throw new NullPointerException("childKey");
          }
          if (value == null) {
              childAttrs.remove(childKey);
          } else {
              childAttrs.put(childKey, value);
          }
          return this;
      }
docs: Set the specific {@link AttributeKey} with the given value on every child {@link Channel}. If the value is
  {@code null} the {@link AttributeKey} is removed