code: @Nullable
    public static Class <?> getPrimitiveClass (@Nullable final Class <?> aClass)
    {
      if (isPrimitiveType (aClass))
        return aClass;
      return WRAPPER_TO_PRIMITIVE.get (aClass);
    }
docs: Get the primitive class of the passed primitive wrapper class.
  
  @param aClass
  The primitive wrapper class. May be <code>null</code>.
  @return <code>null</code> if the passed class is not a primitive wrapper
  class.