sanity/client/SwingSet/src/ButtonDemoScreenshotTest.java failed with "AssertionError: All pixels are not black"

The following test failed in the JDK16 CI:

sanity/client/SwingSet/src/ButtonDemoScreenshotTest.java

Here's a snippet from the log file:

Trace:
Start to wait action "Wait Any javax.swing.JButton loaded (ComponentOperator.WaitComponentTimeout)"
Trace:
"Wait Any javax.swing.JButton loaded (ComponentOperator.WaitComponentTimeout)" action has been produced in 24 milliseconds with result
    : javax.swing.JButton[,69,33,67x25,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.BorderUIResource$CompoundBorderUIResource@1a74e470,flags=296,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=2,left=14,bottom=2,right=14],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Do it,defaultCapable=true]
Saving screenshot to /scratch/opt/mach5/mesos/work_dir/slaves/4076d11c-c6ed-4d07-84c1-4ab8d55cd975-S243796/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/7eca7879-afec-4189-a064-886c6d515d9b/runs/1a271628-9c71-47fb-9fef-d01d4af946e1/testoutput/test-support/jtreg_open_test_jdk_jdk_client_sanity/sanity/client/SwingSet/src/ButtonDemoScreenshotTest/allPixelsAreBlack.png
disposeAllWindows
test ButtonDemoScreenshotTest.test("javax.swing.plaf.metal.MetalLookAndFeel"): failure
java.lang.AssertionError: All pixels are not black
at org.testng.AssertJUnit.fail(AssertJUnit.java:59)
at org.testng.AssertJUnit.assertTrue(AssertJUnit.java:24)
at org.testng.AssertJUnit.assertFalse(AssertJUnit.java:41)
at org.jemmy2ext.JemmyExt.assertNotBlack(JemmyExt.java:96)
at ButtonDemoScreenshotTest.checkButton(ButtonDemoScreenshotTest.java:97)
at ButtonDemoScreenshotTest.test(ButtonDemoScreenshotTest.java:82)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:85)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:639)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:821)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1131)
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:773)
at org.testng.TestRunner.run(TestRunner.java:623)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:357)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:352)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:310)
at org.testng.SuiteRunner.run(SuiteRunner.java:259)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1185)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1110)
at org.testng.TestNG.run(TestNG.java:1018)
at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:94)
at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:54)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
at java.base/java.lang.Thread.run(Thread.java:832)
Trace:
Start to wait frame "Frame with title "JButton Demo"" opened