[Experiment] The email text field from the “Sign In” page is wrongly pre-filled with the “null” string if the “Sign up for Alerts”/”Sign In” button is clicked from any breach from “Breaches” page

[heres-maria-sv-inactive]

[Affected Versions]:

• Firefox Beta Build ID 20200309155231
• Chrome 80.0.3987.149
• Firefox (Fennec) 68.6.0

[Affected Platforms]:

• Windows 10 (x64)
• Android 9 - Samsung Galaxy S8

[Prerequisites]:

• You are on the Breaches page, on any branch.
• You have not performed a breach search, nor have you signed into an account until now.

[Steps to reproduce]:

1. Click the “More about this breach” link.
2. Click the “Sign In” button from the header or the “Sign Up for Alerts” button from the bottom of the page.
3. Observe the email text field.

[Expected results]:

• The field is not pre-filled if a breach search has not been performed and no error messages are displayed.

[Actual results]:

• The field is pre-filled with the string “null” and the “Valid email required” error message is displayed.

[Notes]:

• Attached is a recording of the issue.
  

[heres-maria-sv-inactive]

I have verified that this issue is no longer reproducible using Firefox Beta 75.0b1 Build ID 20200309155231 on Windows 10 (x64), Firefox 23 on iOS 13.3.1 (iPhone 7+), as well as Firefox 68.6.0 on Android 10 (Motorola One Vision).
The null string is no longer displayed.
As a result, I am closing this issue.