SonarQube violation: Unused private method on inner class private constructor

Question

I've used following code in my project. When I evaluated it using sonar it shows Unused private method violation for the private constructor defined in ObjectTypes inner class. If I removed ObjectTypes constructor it shows Hide Utility Class Constructor violation. Please help me to find the best possible way to overcome this issue.

public final class Constants
{
  private Constants()
  {
  }

  public static final String KEY_SEPARATOR = " ~ ";      
  public static final String COMMON_SEPARATOR = " : ";

  public final class ObjectTypes
  {
    private ObjectTypes()
    {
    }
    public static final String ACTION_CODES = "Action Codes";
    public static final String ALL_ACTION_CODES = "All Action Codes";
    //more lines
  }
}

Answer 1

This is the problem:

 private Constants()
  {
  }

And this:

private ObjectTypes()
    {
    }

You do not have to declare EMPTY constructors.