Ah, I had looked for zero, null, and 000 in the DES Wikipedia article but it wasn't mentioned. Didn't think to search for a dedicated article. Thanks!
Saving others a click:
> DES has a few specific keys termed "weak keys" and "semi-weak keys". These are keys that cause the encryption mode of DES to act identically to the decryption mode of DES
Saving others a click:
> DES has a few specific keys termed "weak keys" and "semi-weak keys". These are keys that cause the encryption mode of DES to act identically to the decryption mode of DES