Auto merge of #5885 - bundler:seg-yaml-empty-string-values, r=segiddins
Auto merge of #5885 - bundler:seg-yaml-empty-string-values, r=segiddins

[YAMLSerializer] Handle empty strings properly

### What was the end-user problem that led to this PR?

The problem was that empty strings in YAML were being read in as empty hashes.

Closes https://github.com/bundler/bundler/issues/5881.

### What was your diagnosis of the problem?

My diagnosis was we needed to fix the YAML Serializer to understand `""` as an empty string.

### What is your fix for the problem, implemented in this PR?

My fix ensures that a hash isn't created when the parser encounters `""`.

bundler/bundler,mvz/bundler,dilumnavanjana/bundler,mvz/bundler,bundler/bundler,dilumnavanjana/bundler