NPE in the transition between classes in one test in TestNG (Selenium, Appium)

Question

In the end of creating new test framework on Appium, I have got a trouble. I can't run few test-classes one-by-one. My testng.xml :

    <test name="Test Contact Activity">
        <classes>
            <class name="framework.tests.crm.CRMContactScreenTest"/>
            <class name="framework.tests.crm.CRMAccountScreenTest"/>
        </classes>
    </test>

Currently, result looks like: Result in IDEA

The question is: Why, each run, first class works ok, but in second time appiumDriver get null value. And tests end with NPE:

java.lang.NullPointerException
    at org.openqa.selenium.support.pagefactory.DefaultElementLocator.findElement(DefaultElementLocator.java:69)
    at org.openqa.selenium.support.pagefactory.internal.LocatingElementHandler.invoke(LocatingElementHandler.java:38)
    at com.sun.proxy.$Proxy9.click(Unknown Source)
    at pages.internal.crm.RecentListScreen.goToAccountsList(RecentListScreen.java:89)
    at framework.tests.crm.CRMAccountScreenTest.goToSpecifiedAccount(CRMAccountScreenTest.java:27)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:85)
    at org.testng.internal.Invoker.invokeConfigurationMethod(Invoker.java:552)
    at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:215)
    at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:140)
    at org.testng.internal.Invoker.invokeBeforeGroupsConfigurations(Invoker.java:918)
    at org.testng.internal.Invoker.invokeMethod(Invoker.java:628)
    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:882)
    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1189)
    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:124)
    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:108)
    at org.testng.TestRunner.privateRun(TestRunner.java:767)
    at org.testng.TestRunner.run(TestRunner.java:617)
    at org.testng.SuiteRunner.runTest(SuiteRunner.java:348)
    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:343)
    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:305)
    at org.testng.SuiteRunner.run(SuiteRunner.java:254)
    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
    at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
    at org.testng.TestNG.run(TestNG.java:1057)
    at org.testng.IDEARemoteTestNG.run(IDEARemoteTestNG.java:74)
    at org.testng.RemoteTestNGStarter.main(RemoteTestNGStarter.java:121)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144

)

Answer 1

Have made protected AppiumDriver<WebElement> appiumDriver; in TestBase.class as static . It helps.