Recipient is not parsed from `mailto:` links when given as `mailto:?to=test@example.com`

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Problem

ProtonMail for iOS does not read the mail recipient from mailto: links when the recipient is given via the to parameter. According to RFC 6086, page 6, the recipient can be either given directly after the mailto: or as ?to= parameter. In other words, mailto:?to=test@example.com is equivalent to mailto:test@example.com. ProtonMail handles only the latter form correctly.

Steps to reproduce

1. Setup ProtonMail as the iOS default mail client
2. Open Safari
3. Enter the mailto:?to=test@example.com into the address bar
4. Tap Open
5. Confirm the dialog that you want to open the link in ProtonMail
6. Wait for ProtonMail to open with the new mail panel

Observation: The To address field is empty.

Expectation: The To address field is filled with test@example.com.

Metadata

Proton Mail 4.22.1 (2)