Geeting ERRor for ExtentReports

Hi Ashish,
Could you please let me know why this error was comming.I double checked the extentManager but why this error?

[TestNG] Running:
C:\Users\sanja\AppData\Local\Temp\testng-eclipse-1383916159\testng-customsuite.xml

0
0
FAILED CONFIGURATION: @AfterTest quit
java.lang.NullPointerException
at com.relevantcodes.extentreports.ExtentReports.endTest(ExtentReports.java:618)
at com.Amazon.testcase.ALogin.quit(ALogin.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:85)
at org.testng.internal.Invoker.invokeConfigurationMethod(Invoker.java:510)
at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:211)
at org.testng.internal.Invoker.invokeConfigurations(Invoker.java:138)
at org.testng.TestRunner.afterRun(TestRunner.java:1027)
at org.testng.TestRunner.run(TestRunner.java:627)
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 org.testng.remote.AbstractRemoteTestNG.run(AbstractRemoteTestNG.java:126)
at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:152)
at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:57)


===============================================
Default test
Tests run: 0, Failures: 0, Skips: 0
Configuration Failures: 1, Skips: 0
===============================================


===============================================
Default suite
Total tests run: 0, Failures: 0, Skips: 0
Configuration Failures: 1, Skips: 0
===============================================

[TestNG] Time taken by org.testng.reporters.JUnitReportReporter@4909b8da: 2 ms
[TestNG] Time taken by org.testng.reporters.SuiteHTMLReporter@17550481: 78 ms
[TestNG] Time taken by org.testng.reporters.XMLReporter@68837a77: 9 ms
[TestNG] Time taken by [FailedReporter passed=0 failed=0 skipped=0]: 1 ms
[TestNG] Time taken by org.testng.reporters.EmailableReporter2@15975490: 9 ms
[TestNG] Time taken by org.testng.reporters.jq.Main@2c6a3f77: 58 ms