Combox in grid, if the data text is space, it shows the valu

I have a combox_simple column in my grid. The datasource of the combox contains on option, the value is -1, and the text is " ", a

space. But when I choose the space option, it shows ‘-1’ to me… why? how can I fix this problem?

Which column type do you use: co, coro or combo ?

I use co , thanks

You can try to use   instead of the white space in the xml.

For example: