Empty keys cannot be decoded

[ffried]

I have the following YAML:

root:
  :
    - sub: value1
  other:
    - sub: value2

Which according to YAML Lint is valid.

But Yams fails to decode it with the following error:

2:3: error: parser: while parsing a block mapping in line 2, column 3
did not find expected key:
  :
  ^)))