Powermock not intercepting new object creation

I am attempting to test a method that creates a new instance of another class that I wish to mock using powermock. My code (simplified) is as follows -

Testing code:

import org.junit.runner.RunWith;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

import static org.easymock.EasyMock.anyObject;
import static org.powermock.api.easymock.PowerMock.*;

@RunWith(PowerMockRunner.class)
@PrepareForTest( { ClassUnderTest.class } )
public class TestForClassUnderTest {

    private ClassToBeMocked classToBeMocked;
    private ClassUnderTest classUnderTest;

    public void testSimple() throws Exception {

        classToBeMocked = createMock(ClassToBeMocked.class);
        // trying to intercept the constructor
        // I *think* this is the root cause of the issue 
        expectNew(ClassToBeMocked.class, anyObject(), anyObject(), anyObject()).andReturn(classToBeMocked);

        classToBeMocked.close();
        expectLastCall();
        replayAll();

        // call to perform the test
        classUnderTest.doStuff();
    }
} 

Code that is being tested:

import ClassToBeMocked;

public class ClassUnderTest {
    private ClassToBeMocked classToBeMocked;

    public void doStuff() {

        classToBeMocked = new ClassToBeMocked("A","B","C");
        // doing lots of other things here that I feel are irrelevant
        classToBeMocked.close();
    }
}

Code that I wish to mock:

public class ClassToBeMocked {
    public ClassToBeMocked(String A, String B, String C) {
    // irrelevant
    }
    private close() {
    // irrelevant
    }
}

The error I get is as below:

java.lang.ExceptionInInitializerError

    at ....more inner details of where this goes into

    at ClassToBeMocked.close

    at ClassUnderTest.doStuff

    at TestForClassUnderTest.test.unit.testSimple

Caused by: java.lang.NullPointerException

PowerMock version:1.4.5

EasyMock version: 3.1

PS: I have stripped down the code to bare minimums, only showing the details of the mocking library, let me know if you think my other code is somehow interfering and I can give more details on the bits you think are important to show. Any links to other examples doing this may even help.