Moss spreads over air gaps

The Bug

Moss can spread to nearby blocks even when there is an air gap between the blocks.
Before:

After:

This is similar to MC-214927, but that report is only about blocks which cannot be converted.

Steps to Reproduce

• Build the setup as shown in the attachment below. setup.png
• Apply some bone meal to the moss block.
• Take note as to whether or not the moss spread over air blocks.

Observed Behavior

Moss is able to spread over air blocks.

Expected Behavior

Moss would not be able to spread over air blocks.