Minecraft will not Render In 15w34a and 15w34b

Every time I load in a Minecraft World in the latest two snapshots (15w34a and 15w34b), on the "Loading Chunks" screen, a piece of text flashes before the game renders, and says "0%". Then my game renders the world for a fraction of a second, and the screen goes black. I can still click where the "Save and Quit to Title" button is in the menu and go back to the title screen. Please give me feedback so that I can test out the new command blocks! Thank You. -CREEPERZX2