The /spreadplayers command will spread entities on the structure void block. /spreadplayers commands should not set players onto non solid blocks, such as liquid.

Steps to reproduce

• Run the following command on a superflat with void preset

  /fill 10 -61 6 6 -61 10 minecraft:structure_void

• Run the spreadplayers command

  /spreadplayers 8 8 0 2 false @p

• Observe that you will spawn atop the structure void and fall.
• Replace some of the structure void blocks with solid blocks and observe that you will still be placed above them even though there are possible blocks to spread to.