The wrong error message is displayed when saving an experiment with no value inserted in the Branch - Name section

[Softvision-RemusDranca]

[Affected versions]:

• Firefox Release 66.0.4 and above
• Chrome 74.0. and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have an experiment created on the "https://stage.experimenter.nonprod.dataops.mozgcp.net/" website.
• You are logged in your LDAP account on stage website.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites and navigate to "https://stage.experimenter.nonprod.dataops.mozgcp.net/".
2. Open the created experiment from prerequisites.
3. Click the "Edit" button from "Branches" section.
4. Delete the value from the "Name" input field.
5. Click the "Save Draft" button and observe the behavior.

[Expected result]:

• The "! This field is required" error message is displayed.

[Actual result]:

• The "! All branches must have a unique name" error message is displayed.

[Notes]:

• This issue is reproducible if empty spaces are inserted in the "Name" input field.
• This issue is also reproducible if two or more branches are created. If one of the "Name" input field has no value inserted and the other ones have different names inserted. After saving the experiment the "! All branches must have a unique name" error message is displayed for all "Name" input fields.
• Attached is a screen recording of the issue:

[Softvision-RemusDranca]

I have verified this issue and is no longer reproducible on Experimenter stage "https://stage.experimenter.nonprod.dataops.mozgcp.net/" website after the v2.28.2 stage deployment. Tested on Windows 10x64, Mac 10.14 and Arch Linux 4.16.6 x64.