Unable to call newInstance() on dynamically generated class

Question

I am starting to use asm for generating classes at runtime. I started with a very simple class, which has just one String field and a getter for the same.

ClassWriter cw = new ClassWriter(0);
String Name = "Sample";
            cw.visit(Opcodes.V1_5, Opcodes.ACC_PUBLIC ,
                    Name, null,"java/lang/Object",
                    new String[] {});
                    cw.visitField(Opcodes.ACC_PRIVATE, "punit", "Ljava/lang/String;",
                    null, "sac").visitEnd();
            MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "getUnit",
                    "()Ljava/lang/String;", null, null);

            mv.visitCode();
            mv.visitVarInsn(Opcodes.ALOAD, 0);
            mv.visitFieldInsn(Opcodes.GETFIELD, destinationName+"Configuration", "unit", "Ljava/lang/String;");
            mv.visitInsn(Opcodes.ARETURN);
            mv.visitMaxs(1, 1);
            mv.visitEnd();           
            cw.visitEnd();

            byte[] b = cw.toByteArray();

After the byte array is created I create a custom classLoader & called its defineClass method to get hold of the Class object.

Then I call newInstance() on this object but I get an InstantiationException. When I debugged the code I found that it is not finding a constructor for the newly created class!

Should I generate a constructor for the class as well?