Plugin does not work with library build, error: cannot find symbol Env

I've been using this plugin successfully before, but now I cannot get it to work on a new project.

In this project I am building an Android library that should use dotenv for configuration (in the subfolder library) , as well as a demo application that uses the library (app).

In my library/build.gradle I have:

plugins {
    id 'com.android.library'
    id 'maven-publish'
    id "earth.levi.dotenv-android" version "1.3.0"
}

dotenv {
    packageName = "com.example.library"
    sourcePath = "src/main/java/"
}

With my main code at ./library/src/main/java/com/example/library/Foo.java, which contains a reference to Env.foo.

In .env, I have:

FOO=bar

In my ./settings.gradle, I have:

// ...
rootProject.name = "library"
include ':app'
include ':library'

Now when I run:

./gradlew build

I get:

> Task :library:compileDebugJavaWithJavac FAILED
/testproject/library/src/main/java/com/example/library/Foo.java:711: error: cannot find symbol
            mFoo = Env.foo;
                       ^
  symbol:   variable Env
  location: class Builder

...

FAILURE: Build failed with an exception.

I also do not see any tasks related to dotenv when I run ./gradlew tasks.

Any idea why this would not work?

Start with library/build.gradle and the dotenv plugin configuration, then run ./gradlew tasks and ./gradlew build to compare the library module's tasks and compilation output. Check whether Env is generated under library/src/main/java/com/example/library and whether the library compile task sees it; done means the library builds with Foo.java resolving Env and the expected dotenv task is present.