[ruby-core:95944] [Ruby master Bug#16368] Error in `YAML.load(symbolize_names: true)` with null column YAML

[ruby-core:95944] [Ruby master Bug#16368] Error in `YAML.load(symbolize_names: true)` with null column YAML

[uzukifirst]

Issue #16368 has been reported by kibitan (Chikahiro Tokoro).

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Bug #16368: Error in `YAML.load(symbolize_names: true)` with null column YAML
https://bugs.ruby-lang.org/issues/16368

* Author: kibitan (Chikahiro Tokoro)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.7.0preview2 (2019-10-22 master 02aadf1032) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
Trying to parse YAML which contains null column `symbolize_names: true` would raise `NoMethodError`


```
irb(main):001:0> require 'yaml'
=> true
irb(main):002:0> YAML.load("null: nullnull")
=> {nil=>"nullnull"}
irb(main):003:0> YAML.load("null: nullnull", symbolize_names: true)
Traceback (most recent call last):
        8: from /usr/local/bin/irb:23:in `<main>'
        7: from /usr/local/bin/irb:23:in `load'
        6: from /usr/local/lib/ruby/gems/2.7.0/gems/irb-1.1.0.pre.3/exe/irb:11:in `<top (required)>'
        5: from (irb):4
        4: from /usr/local/lib/ruby/2.7.0/psych.rb:276:in `load'
        3: from /usr/local/lib/ruby/2.7.0/psych.rb:606:in `symbolize_names!'
        2: from /usr/local/lib/ruby/2.7.0/psych.rb:606:in `each'
        1: from /usr/local/lib/ruby/2.7.0/psych.rb:607:in `block in symbolize_names!'
NoMethodError (undefined method `to_sym' for nil:NilClass
```


I also send a pull request for related repo.
https://github.com/ruby/psych/pull/423



-- 
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