code: @Nonnull
    public EChange addUniqueVariable (@Nonnull final QName aName, @Nonnull final Object aValue)
    {
      ValueEnforcer.notNull (aName, "Name");
      ValueEnforcer.notNull (aValue, "Value");
  
      if (m_aMap.containsKey (aName))
        return EChange.UNCHANGED;
      m_aMap.put (aName, aValue);
      return EChange.CHANGED;
    }
docs: Add a new variable.
  
  @param aName
  The qualified name of the variable
  @param aValue
  The value to be used.
  @return {@link EChange}