So first you create an empty map using the [:] notation.

所以首先要使用[：]符号创建一个空映射。

youdao

If you leave a String field blank in an HTML form, it comes back to the controller in the params Map as an empty String (that is, ) instead of null.

如果在HTML表单中将String字段保留为空，params map中的控制器会将其看作空string(也就是“ ”)，而不是null。

youdao

But it's not completely empty, as a new map of the interstellar space in the 1, 000 light-years around the sun shows.

但它又不是完全的空无一物，正如这张最新的太阳周边1000光年范围内星际空间地图所示。

youdao