We added the one field[CVE IDENTIFIER] to the Filter,Report Issue and Issue detail page through the plugin.

While creating/updating the mantis incident the user can enter any value to the text field for the field[CVE IDENTIFIER] but this field is not mandatory so the user can set it as blank also.
In the filter page we have added this field having a type "FILTER_TYPE_MULTI_STRING". So now the filter displays all the value added to this field while creating/updating the incidents. By default this filter have a "any" field in the dropdown.
So if the user wants to get the list of all incident in which we have not set any value to the field[CVE IDENTIFIER], than the user will select the blank field from the dropdown to get the desired results but after applying the filter user get the desired result but on filter page it dispaly the "any" text selected in the filter page for this field.