"Hollow vegetable" is not a derogatory term, it actually refers to a common vegetable in life, because of its thicker stem, the inner hollow and named. In Cantonese-speaking areas, people affectionately refer to the "hollow vegetable" as "Tongcai".
To say that a person is like a "hollow cabbage" is not to say that he looks like a vegetable, but to describe him as a person who is more simple and has no heart. This kind of person is just like the hollow cabbage, the exterior seems to be full, in fact, there is no content in the heart. They don't have their own opinions and are easily swayed by others and go with the flow.
The "emptiness" of the cabbage also has a positive side. It represents a simple and straightforward character. Hollow people tend to be very sincere, they don't play tricks, they don't love to calculate, and they are very comfortable to get along with. They are like a clear lake that looks down to the bottom, allowing people to see through them at a glance.
Imagine if you have such a "hollow" friend beside you, what a happy thing it would be! They don't fight, and they don't talk behind your back. They are like a ray of sunshine that brightens your life.
So don't be angry when someone says you're "hollow", it's not a pejorative, but perhaps even a compliment. It may even be a compliment, because it reflects your simplicity and goodness. If you want to become more opinionated and thoughtful, then you may want to read more, think more, broaden your horizons and enrich your inner world.