NullPointerException when running sample projects

NullPointerException is thrown when running sample project using Drools and Java Runtime classes because KieSession is not created.

Eclipse log:
!SESSION 2017-04-04 12:39:38.638 -----------------------------------------------
eclipse.buildId=4.6.3.M20170301-0400
java.version=1.8.0_121
java.vendor=Oracle Corporation
BootLoader constants: OS=linux, ARCH=x86_64, WS=gtk, NL=en_US
Framework arguments: -product org.eclipse.epp.package.jee.product
Command-line arguments: -os linux -ws gtk -arch x86_64 -product org.eclipse.epp.package.jee.product

!ENTRY org.drools.eclipse 4 120 2017-04-04 12:41:31.737
!MESSAGE Internal error in Drools Plugin:
!STACK 1
Java Model Exception: Java Model Status [Build path contains duplicate entry: 'DROOLS/Drools' for project 'TestProject']
at org.eclipse.jdt.internal.core.JavaModelOperation.runOperation(JavaModelOperation.java:786)
at org.eclipse.jdt.internal.core.JavaProject.setRawClasspath(JavaProject.java:3097)
at org.eclipse.jdt.internal.core.JavaProject.setRawClasspath(JavaProject.java:3059)
at org.eclipse.jdt.internal.core.JavaProject.setRawClasspath(JavaProject.java:3112)
at org.drools.eclipse.util.DroolsRuntimeManager.addBuilder(DroolsRuntimeManager.java:122)
at org.drools.eclipse.action.ConvertToDroolsProjectAction.run(ConvertToDroolsProjectAction.java:45)
at org.eclipse.ui.internal.PluginAction.runWithEvent(PluginAction.java:247)
at org.eclipse.jface.action.ActionContributionItem.handleWidgetSelection(ActionContributionItem.java:565)
at org.eclipse.jface.action.ActionContributionItem.lambda$4(ActionContributionItem.java:397)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:5227)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1340)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4561)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:4151)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$4.run(PartRenderingEngine.java:1121)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1022)
at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:150)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:693)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:336)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:610)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:148)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:138)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:388)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:243)
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:498)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:673)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:610)
at org.eclipse.equinox.launcher.Main.run(Main.java:1519)
at org.eclipse.equinox.launcher.Main.main(Main.java:1492)
!SUBENTRY 1 org.eclipse.jdt.core 4 977 2017-04-04 12:41:31.739
!MESSAGE Build path contains duplicate entry: 'DROOLS/Drools' for project 'TestProject'