Can't figure out how to set a user property in analytics

[j05u3]

There is this method,which I believe doesn't work. Or at least I can't figure out how to use because I couldn't find a way to instantiate this class

Dart version: 2.8.0

OS: windows

Package version: 7.2.1

Flutter doctor just in case (because I am trying to use the package in a flutter web project):

[√] Flutter (Channel dev, v1.16.1, on Microsoft Windows [Version 10.0.18363.752], locale en-US)
    • Flutter version 1.16.1 at C:\dev\flutter
    • Framework revision e6b0f5f238 (11 days ago), 2020-03-18 21:56:02 -0400
    • Engine revision 216c420a2c
    • Dart version 2.8.0 (build 2.8.0-dev.15.0 96cf889e6b)


[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at C:\dev\android_home
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.2
    • ANDROID_HOME = C:\dev\android_home
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 3.6)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin version 44.0.2
    • Dart plugin version 192.7761
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)

[√] VS Code (version 1.43.2)
    • VS Code at C:\Users\josue\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.8.1

[√] Connected device (2 available)
    • Chrome     • chrome     • web-javascript • Google Chrome 80.0.3987.149
    • Web Server • web-server • web-javascript • Flutter Tools

• No issues found!