java.lang.AssertionError
        at org.netbeans.api.java.source.GeneratorUtilities.insertClassMember(GeneratorUtilities.java:131)
        at org.netbeans.modules.refactoring.java.plugins.EncapsulateFieldRefactoringPlugin$Encapsulator.createGetterAndSetter(EncapsulateFieldRefactoringPlugin.java:863)
        at org.netbeans.modules.refactoring.java.plugins.EncapsulateFieldRefactoringPlugin$Encapsulator.visitClass(EncapsulateFieldRefactoringPlugin.java:564)
        at org.netbeans.modules.refactoring.java.plugins.EncapsulateFieldRefactoringPlugin$Encapsulator.visitClass(EncapsulateFieldRefactoringPlugin.java:513)
        at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:605)
        at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:67)
        at com.sun.source.util.TreeScanner.scan(TreeScanner.java:90)
        at org.netbeans.modules.refactoring.java.plugins.EncapsulateFieldRefactoringPlugin$Encapsulator.visitCompilationUnit(EncapsulateFieldRefactoringPlugin.java:545)
        at org.netbeans.modules.refactoring.java.plugins.EncapsulateFieldRefactoringPlugin$Encapsulator.visitCompilationUnit(EncapsulateFieldRefactoringPlugin.java:513)
        at com.sun.tools.javac.tree.JCTree$JCCompilationUnit.accept(JCTree.java:483)
        at com.sun.source.util.TreePathScanner.scan(TreePathScanner.java:67)
        at org.netbeans.modules.refactoring.java.spi.JavaRefactoringPlugin$TransformTask.run(JavaRefactoringPlugin.java:363)
        at org.netbeans.modules.refactoring.java.spi.JavaRefactoringPlugin$TransformTask.run(JavaRefactoringPlugin.java:333)
        at org.netbeans.api.java.source.JavaSource.runModificationTask(JavaSource.java:915)
        at org.netbeans.modules.refactoring.java.spi.JavaRefactoringPlugin.processFiles(JavaRefactoringPlugin.java:244)
        at org.netbeans.modules.refactoring.java.spi.JavaRefactoringPlugin.createAndAddElements(JavaRefactoringPlugin.java:254)
        at org.netbeans.modules.refactoring.java.spi.JavaRefactoringPlugin.createAndAddElements(JavaRefactoringPlugin.java:270)
        at org.netbeans.modules.refactoring.java.plugins.EncapsulateFieldsPlugin.prepare(EncapsulateFieldsPlugin.java:190)
        at org.netbeans.modules.refactoring.api.AbstractRefactoring.pluginsPrepare(AbstractRefactoring.java:380)
        at org.netbeans.modules.refactoring.api.AbstractRefactoring.prepare(AbstractRefactoring.java:202)
        at org.netbeans.modules.refactoring.spi.impl.ParametersPanel$Prepare.run(ParametersPanel.java:765)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:561)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:986)