[ruby-core:74527] [Ruby trunk Bug#12212] Parsing a URI of "mailto:?subject=hi" with `URI.parse` raises an exception

Issue #12212 has been reported by Mark Dodwell.

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Bug #12212: Parsing a URI of "mailto:?subject=hi" with `URI.parse` raises an exception
https://bugs.ruby-lang.org/issues/12212

* Author: Mark Dodwell
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: trunk
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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Parsing a URI of "mailto:?subject=hi" with `URI.parse` raises an exception. I believe this is a valid "mailto" URI, as defined in RFC6068.

Behavior observed:

```ruby
>> URI.parse("mailto:?subject=hi")
NoMethodError: undefined method `split' for nil:NilClass
```

Behavior expected:

```ruby
>> uri = URI.parse("mailto:?subject=hi")
=> #<URI::MailTo URL:mailto:?subject=hi>
>> uri.to
=> ""
>> uri.headers
=> [["subject", "hi"]]
```

Reference from RFC6068 than defines the "to" element as optional:

> mailtoURI = "mailto:" [ to ] [ hfields ]
>
> https://tools.ietf.org/html/rfc6068#section-2

Patch attached.

---Files--------------------------------
fix-uri-mailto-parsing-blank-to-with-query.patch (1.52 KB)


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