Custom locator strategy in appium with the Test.AI plugin: "Unsupported locator strategy: -custom"

I'm trying to run the test.ai plugin for appium (https://github.com/testdotai/appium-classifier-plugin). It has a custom locator strategy. I set up appium and did:

'npm install -g test-ai-classifier'

it was installed, as shown:

https://i.stack.imgur.com/fwtkt.png

I then wrote a simple test to check if everything is set up correctly:

import io.appium.java_client.AppiumDriver;
import io.appium.java_client.android.AndroidDriver;
import io.appium.java_client.remote.MobileCapabilityType;
import io.appium.java_client.MobileBy;
import io.appium.java_client.MobileElement;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;

import org.junit.Before;
import org.junit.After;
import org.junit.Test;
import org.openqa.selenium.By;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.remote.DesiredCapabilities;

public class TestClass {

    private AppiumDriver driver;
    private By cart = MobileBy.custom("cart");

    @Before
    public void setUp() throws MalformedURLException {
        DesiredCapabilities capabilities = new DesiredCapabilities();

        capabilities.setCapability(MobileCapabilityType.PLATFORM_NAME, "Android");
        capabilities.setCapability(MobileCapabilityType.PLATFORM_VERSION, "9");
        capabilities.setCapability(MobileCapabilityType.DEVICE_NAME, "NB1GAD17B1504154");
        capabilities.setCapability(MobileCapabilityType.BROWSER_NAME, "Chrome");

        HashMap<String, String> customFindModules = new HashMap<String, String>();
        customFindModules.put("ai", "test-ai-classifier");

        capabilities.setCapability("customFindModules", customFindModules);
        capabilities.setCapability("shouldUseCompactResponses", false);

        driver = new AndroidDriver(new URL("http://localhost:4723/wd/hub"), capabilities);
    }

    @After
    public void tearDown(){

    }

    @Test
    public void testMethod(){
        goToWebsite(driver);
        openCartUseAi(driver);
    }

    public void goToWebsite(AppiumDriver driver){
        driver.get("https://www.ebay.com/");

    }

    public void openCartUseAi(AppiumDriver driver){
        driver.findElement(cart).click();
    }



}

This causes the following error when ran:

/usr/lib/jvm/java-1.11.0-openjdk-amd64/bin/java -ea -Didea.test.cyclic.buffer.size=1048576 -javaagent:/home/piotrek/intellij/ideaIC-2019.1.2/idea-IC-191.7141.44/lib/idea_rt.jar=38561:/home/piotrek/intellij/ideaIC-2019.1.2/idea-IC-191.7141.44/bin -Dfile.encoding=UTF-8 -classpath /home/piotrek/intellij/ideaIC-2019.1.2/idea-IC-191.7141.44/lib/idea_rt.jar:/home/piotrek/intellij/ideaIC-2019.1.2/idea-IC-191.7141.44/plugins/junit/lib/junit-rt.jar:/home/piotrek/intellij/ideaIC-2019.1.2/idea-IC-191.7141.44/plugins/junit/lib/junit5-rt.jar:/home/piotrek/IdeaProjects/appiumTestMVN/target/test-classes:/home/piotrek/Downloads/selenium-server-standalone-3.141.59.jar:/home/piotrek/.m2/repository/io/appium/java-client/7.0.0/java-client-7.0.0.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-java/3.141.59/selenium-java-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-chrome-driver/3.141.59/selenium-chrome-driver-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-edge-driver/3.141.59/selenium-edge-driver-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-firefox-driver/3.141.59/selenium-firefox-driver-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-ie-driver/3.141.59/selenium-ie-driver-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-opera-driver/3.141.59/selenium-opera-driver-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-remote-driver/3.141.59/selenium-remote-driver-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-safari-driver/3.141.59/selenium-safari-driver-3.141.59.jar:/home/piotrek/.m2/repository/net/bytebuddy/byte-buddy/1.8.15/byte-buddy-1.8.15.jar:/home/piotrek/.m2/repository/org/apache/commons/commons-exec/1.3/commons-exec-1.3.jar:/home/piotrek/.m2/repository/com/google/guava/guava/25.0-jre/guava-25.0-jre.jar:/home/piotrek/.m2/repository/com/google/code/findbugs/jsr305/1.3.9/jsr305-1.3.9.jar:/home/piotrek/.m2/repository/org/checkerframework/checker-compat-qual/2.0.0/checker-compat-qual-2.0.0.jar:/home/piotrek/.m2/repository/com/google/errorprone/error_prone_annotations/2.1.3/error_prone_annotations-2.1.3.jar:/home/piotrek/.m2/repository/com/google/j2objc/j2objc-annotations/1.1/j2objc-annotations-1.1.jar:/home/piotrek/.m2/repository/org/codehaus/mojo/animal-sniffer-annotations/1.14/animal-sniffer-annotations-1.14.jar:/home/piotrek/.m2/repository/com/squareup/okhttp3/okhttp/3.11.0/okhttp-3.11.0.jar:/home/piotrek/.m2/repository/com/squareup/okio/okio/1.14.0/okio-1.14.0.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-support/3.141.59/selenium-support-3.141.59.jar:/home/piotrek/.m2/repository/org/seleniumhq/selenium/selenium-api/3.141.59/selenium-api-3.141.59.jar:/home/piotrek/.m2/repository/com/google/code/gson/gson/2.8.5/gson-2.8.5.jar:/home/piotrek/.m2/repository/org/apache/httpcomponents/httpclient/4.5.6/httpclient-4.5.6.jar:/home/piotrek/.m2/repository/org/apache/httpcomponents/httpcore/4.4.10/httpcore-4.4.10.jar:/home/piotrek/.m2/repository/commons-logging/commons-logging/1.2/commons-logging-1.2.jar:/home/piotrek/.m2/repository/commons-codec/commons-codec/1.10/commons-codec-1.10.jar:/home/piotrek/.m2/repository/cglib/cglib/3.2.8/cglib-3.2.8.jar:/home/piotrek/.m2/repository/org/ow2/asm/asm/6.2.1/asm-6.2.1.jar:/home/piotrek/.m2/repository/org/apache/ant/ant/1.10.3/ant-1.10.3.jar:/home/piotrek/.m2/repository/org/apache/ant/ant-launcher/1.10.3/ant-launcher-1.10.3.jar:/home/piotrek/.m2/repository/commons-validator/commons-validator/1.6/commons-validator-1.6.jar:/home/piotrek/.m2/repository/commons-beanutils/commons-beanutils/1.9.2/commons-beanutils-1.9.2.jar:/home/piotrek/.m2/repository/commons-digester/commons-digester/1.8.1/commons-digester-1.8.1.jar:/home/piotrek/.m2/repository/commons-collections/commons-collections/3.2.2/commons-collections-3.2.2.jar:/home/piotrek/.m2/repository/org/apache/commons/commons-lang3/3.8/commons-lang3-3.8.jar:/home/piotrek/.m2/repository/commons-io/commons-io/2.6/commons-io-2.6.jar:/home/piotrek/.m2/repository/org/springframework/spring-context/5.1.0.RELEASE/spring-context-5.1.0.RELEASE.jar:/home/piotrek/.m2/repository/org/springframework/spring-aop/5.1.0.RELEASE/spring-aop-5.1.0.RELEASE.jar:/home/piotrek/.m2/repository/org/springframework/spring-beans/5.1.0.RELEASE/spring-beans-5.1.0.RELEASE.jar:/home/piotrek/.m2/repository/org/springframework/spring-core/5.1.0.RELEASE/spring-core-5.1.0.RELEASE.jar:/home/piotrek/.m2/repository/org/springframework/spring-jcl/5.1.0.RELEASE/spring-jcl-5.1.0.RELEASE.jar:/home/piotrek/.m2/repository/org/springframework/spring-expression/5.1.0.RELEASE/spring-expression-5.1.0.RELEASE.jar:/home/piotrek/.m2/repository/org/aspectj/aspectjweaver/1.9.1/aspectjweaver-1.9.1.jar:/home/piotrek/.m2/repository/org/slf4j/slf4j-api/1.7.25/slf4j-api-1.7.25.jar:/home/piotrek/.m2/repository/junit/junit/4.12/junit-4.12.jar:/home/piotrek/.m2/repository/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 TestClass,testMethod
Jun 07, 2019 10:34:10 AM io.appium.java_client.remote.AppiumCommandExecutor$1 lambda$0
INFO: Detected dialect: W3C

org.openqa.selenium.InvalidArgumentException: invalid argument: Unsupported locator strategy: -custom
  (Session info: chrome=74.0.3729.157)
  (Driver info: chromedriver=2.46.628388 (4a34a70827ac54148e092aafb70504c4ea7ae926),platform=Linux 5.0.0-15-generic x86_64)
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:25:53'
System info: host: 'piotrek-VirtualBox', ip: '127.0.1.1', os.name: 'Linux', os.arch: 'amd64', os.version: '5.0.0-15-generic', java.version: '11.0.3'
Driver info: io.appium.java_client.android.AndroidDriver
Capabilities {browserName: Chrome, customFindModules: {ai: test-ai-classifier}, databaseEnabled: false, desired: {browserName: Chrome, customFindModules: {ai: test-ai-classifier}, deviceName: NB1GAD17B1504154, platformName: android, platformVersion: 9, shouldUseCompactResponses: false}, deviceManufacturer: HMD Global, deviceModel: TA-1004, deviceName: NB1GAD17B1504154, deviceScreenSize: 1440x2560, deviceUDID: NB1GAD17B1504154, javascriptEnabled: true, locationContextEnabled: false, networkConnectionEnabled: true, platform: LINUX, platformName: Android, platformVersion: 9, shouldUseCompactResponses: false, takesScreenshot: true, warnings: {}, webStorageEnabled: false}
Session ID: dbae9abd-649a-4b95-80a8-1dccbf8e692b
*** Element info: {Using=-custom, value=cart}

    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490)
    at org.openqa.selenium.remote.http.W3CHttpResponseCodec.createException(W3CHttpResponseCodec.java:187)
    at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:122)
    at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:49)
    at org.openqa.selenium.remote.HttpCommandExecutor.execute(HttpCommandExecutor.java:158)
    at io.appium.java_client.remote.AppiumCommandExecutor.execute(AppiumCommandExecutor.java:239)
    at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:552)
    at io.appium.java_client.DefaultGenericMobileDriver.execute(DefaultGenericMobileDriver.java:42)
    at io.appium.java_client.AppiumDriver.execute(AppiumDriver.java:1)
    at io.appium.java_client.android.AndroidDriver.execute(AndroidDriver.java:1)
    at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:323)
    at io.appium.java_client.DefaultGenericMobileDriver.findElement(DefaultGenericMobileDriver.java:62)
    at io.appium.java_client.AppiumDriver.findElement(AppiumDriver.java:1)
    at io.appium.java_client.android.AndroidDriver.findElement(AndroidDriver.java:1)
    at io.appium.java_client.FindsByCustom.findElementByCustom(FindsByCustom.java:38)
    at io.appium.java_client.MobileBy$ByCustom.findElement(MobileBy.java:631)
    at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:315)
    at io.appium.java_client.DefaultGenericMobileDriver.findElement(DefaultGenericMobileDriver.java:58)
    at io.appium.java_client.AppiumDriver.findElement(AppiumDriver.java:1)
    at io.appium.java_client.android.AndroidDriver.findElement(AndroidDriver.java:1)
    at TestClass.openCartUseAi(TestClass.java:62)
    at TestClass.testMethod(TestClass.java:49)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intel

lij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)


Process finished with exit code 255

Can anyone tell me what I'm doing wrong? When rewriting this test to not use the plugin, everything works fine, so Appium is set up correctly.

I had a look at this doc, but still can't see what I'm missing: http://appium.io/docs/en/advanced-concepts/element-finding-plugins/

Thank You in advance for your help!

PS not sure if this is relevant, but I'm using an Ubuntu virtual machine for this