Pick block doesn't work on Iron Golems, Snow Golems, Withers, and Ender Dragons

Summary:
When using pick block on an iron golem, snow golem, ender dragon, or a wither, the player isn't given a spawn egg.

Steps to Reproduce:

1. Spawn an iron golem, snow golem, ender dragon, and a wither in Creative mode
2. Press the pick block button while looking at these mobs

Observed Results:
Nothing happens.

Expected Results:
A spawn egg should be given.