code: @Nonnull
    public EChange remove (@Nullable final String sVarName)
    {
      if (StringHelper.hasText (sVarName))
        if (m_aMap.remove (PSXPathQueryBinding.PARAM_VARIABLE_PREFIX + sVarName) == null)
          return EChange.CHANGED;
      return EChange.UNCHANGED;
    }
docs: Remove the variable with the specified name
  
  @param sVarName
  The name of the variable to be removed. May be <code>null</code>.
  @return {@link EChange#CHANGED} if the variable was removed successfully.
  Never <code>null</code>.