powermockito.mockstatic не работает при сборке с использованием Ant

public class MainClass {
    public void userValidation() {
    Utils.isNameExist();
    };
}

public class Utils {
    public static String isNameExist() {
        Boolean isExist = false;
        //get name value from UserEnum enum object
        if(UserEnum.NAME.value().equal("Me")) {
            isExist = true;
        }
    }
}

public enum UserEnum {
    NAME("NM");
    private String val;
    private UserEnum (final String Value){
        this.val = value;
    }
    public String value(){
        return val;
    }
}

@RunWith(PowerMockRunner.class)
@PrepareForTest({Utils.class})
public class MainClassTest {
    MainClass mainClass;

    @Before
    public void setUp() throws Exception() {
        mainClass = new MainClass();
    }

    @Test
    public void testUserValidation() {
        PowerMockito.mockStatic(Utils.class);
        when(Utils.isNameExist()).thenReturn(true);
        mainClass.userValidation();
    }
}

Вышеприведенный код отлично работает в Eclipse. Я получаю сообщение об ошибке только при попытке сборки с помощью Ant. Я заметил, что если я удаляю код, связанный с Enum, то сборка Ant работает нормально. Каким-то образом Enum создает проблему. Кто-нибудь может мне помочь.

Баночка использовалась:

javassist-3.4.GA.jar
powermock-easymock-1.4.5-full.jar
powermock-mockito-1.4.6-full.jar
junit-4.4.jar
mockito-all-1.9.0.jar

Error:

[junit]     Caused an ERROR
    [junit] Failed to transform class with name com.Utils$UserEnum. Reason: null
    [junit] java.lang.IllegalStateException: Failed to transform class with name com.Utils$UserEnum. Reason: null
    [junit]     at org.powermock.core.classloader.MockClassLoader.loadMockClass(MockClassLoader.java:208)
    [junit]     at org.powermock.core.classloader.MockClassLoader.loadModifiedClass(MockClassLoader.java:146)
    [junit]     at org.powermock.core.classloader.DeferSupportingClassLoader.loadClass(DeferSupportingClassLoader.java:65)
    [junit]     at java.lang.ClassLoader.loadClass(ClassLoader.java:597)
    [junit]     at java.lang.Class.getDeclaredMethodsImpl(Native Method)
    [junit]     at java.lang.Class.getDeclaredMethods(Class.java:664)
    [junit]     at org.mockito.cglib.core.ReflectUtils.addAllMethods(ReflectUtils.java:349)
    [junit]     at org.mockito.cglib.proxy.Enhancer.getMethods(Enhancer.java:422)
    [junit]     at org.mockito.cglib.proxy.Enhancer.generateClass(Enhancer.java:457)
    [junit]     at org.mockito.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
    [junit]     at org.mockito.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:217)
    [junit]     at org.mockito.cglib.proxy.Enhancer.createHelper(Enhancer.java:378)
    [junit]     at org.mockito.cglib.proxy.Enhancer.createClass(Enhancer.java:318)
    [junit]     at org.mockito.internal.creation.jmock.ClassImposterizer.createProxyClass(ClassImposterizer.java:93)
    [junit]     at org.mockito.internal.creation.jmock.ClassImposterizer.imposterise(ClassImposterizer.java:50)
    [junit]     at org.powermock.api.mockito.internal.mockcreation.MockCreator.createMethodInvocationControl(MockCreator.java:100)
    [junit]     at org.powermock.api.mockito.internal.mockcreation.MockCreator.mock(MockCreator.java:54)
    [junit]     at org.powermock.api.mockito.PowerMockito.mockStatic(PowerMockito.java:70)    org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:322)
    [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:309)
    [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:297)
    [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:222)
    [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:161)
    [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:135)
    [junit]     at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:133)
    [junit]     at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:112)
    [junit]     at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:57)
    [junit] Caused by: java.lang.NullPointerException
    [junit]     at javassist.compiler.MemberResolver.lookupMethod(MemberResolver.java:110)
    [junit]     at javassist.compiler.MemberResolver.lookupMethod(MemberResolver.java:96)
    [junit]     at javassist.compiler.TypeChecker.atMethodCallCore(TypeChecker.java:704)
    [junit]     at javassist.compiler.TypeChecker.atCallExpr(TypeChecker.java:681)
    [junit]     at javassist.compiler.JvstTypeChecker.atCallExpr(JvstTypeChecker.java:156)
    [junit]     at javassist.compiler.ast.CallExpr.accept(CallExpr.java:45)
    [junit]     at javassist.compiler.Javac$1.setReturnType(Javac.java:449)
    [junit]     at javassist.compiler.JvstTypeChecker.atCallExpr(JvstTypeChecker.java:146)
    [junit]     at javassist.compiler.ast.CallExpr.accept(CallExpr.java:45)
    [junit]     at javassist.compiler.TypeChecker.atVariableAssign(TypeChecker.java:248)
    [junit]     at javassist.compiler.TypeChecker.atAssignExpr(TypeChecker.java:217)
    [junit]     at javassist.compiler.ast.AssignExpr.accept(AssignExpr.java:38)
    [junit]     at javassist.compiler.CodeGen.doTypeCheck(CodeGen.java:235)
    [junit]     at javassist.compiler.CodeGen.atStmnt(CodeGen.java:323)
    [junit]     at javassist.compiler.ast.Stmnt.accept(Stmnt.java:49)
    [junit]     at javassist.compiler.CodeGen.atStmnt(CodeGen.java:344)
    [junit]     at javassist.compiler.ast.Stmnt.accept(Stmnt.java:49)
    [junit]     at javassist.compiler.CodeGen.atIfStmnt(CodeGen.java:384)
    [junit]     at javassist.compiler.CodeGen.atStmnt(CodeGen.java:348)
    [junit]     at javassist.compiler.ast.Stmnt.accept(Stmnt.java:49)
    [junit]     at javassist.compiler.CodeGen.atStmnt(CodeGen.java:344)
    [junit]     at javassist.compiler.ast.Stmnt.accept(Stmnt.java:49)
    [junit]     at javassist.compiler.Javac.compileStmnt(Javac.java:558)
    [junit]     at javassist.expr.MethodCall.replace(MethodCall.java:233)
    [junit]     at org.powermock.core.transformers.impl.MainMockTransformer$PowerMockExpressionEditor.edit(MainMockTransformer.java:257)
    [junit]     at javassist.expr.ExprEditor.loopBody(ExprEditor.java:178)
    [junit]     at javassist.expr.ExprEditor.doit(ExprEditor.java:90)
    [junit]     at javassist.CtClassType.instrument(CtClassType.java:1224)
    [junit]     at org.powermock.core.transformers.impl.MainMockTransformer.transform(MainMockTransformer.java:70)
    [junit]     at org.powermock.core.classloader.MockClassLoader.loadMockClass(MockClassLoader.java:204)
    [junit] 
BUILD FAILED