How to use the pywps.exceptions.InvalidParameterValue function in pywps

def __init__(self, reference=None, values_form=None):
        self.reference = reference
        self.values_form = values_form

        if not self.reference:
            raise InvalidParameterValue("values reference is missing.")

wpsrequest.store_execute = response_document[
                    0].attrib.get('storeExecuteResponse', 'false')
                wpsrequest.status = response_document[
                    0].attrib.get('status', 'false')

        if tagname == self.WPS.GetCapabilities().tag:
            self.operation = 'getcapabilities'
            return parse_post_getcapabilities
        elif tagname == self.WPS.DescribeProcess().tag:
            self.operation = 'describeprocess'
            return parse_post_describeprocess
        elif tagname == self.WPS.Execute().tag:
            self.operation = 'execute'
            return parse_post_execute
        else:
            raise InvalidParameterValue(
                'Unknown request %r' % tagname, 'request')

def _get_request(self):
        """HTTP GET request parser
        """

        # service shall be WPS
        service = _get_get_param(self.http_request, 'service')
        if service:
            if str(service).lower() != 'wps':
                raise InvalidParameterValue(
                    'parameter SERVICE [%s] not supported' % service, 'service')
        else:
            raise MissingParameterValue('service', 'service')

        operation = _get_get_param(self.http_request, 'request')

        request_parser = self._get_request_parser(operation)
        request_parser(self.http_request)

# catch error generated by process code
        try:
            wps_response = process.execute(wps_request)
        except Exception as e:
            raise NoApplicableCode('Service error: %s' % e)

        # get the specified output as raw
        if wps_request.raw:
            for outpt in wps_request.outputs:
                for proc_outpt in process.outputs:
                    if outpt == proc_outpt.identifier:
                        return Response(proc_outpt.data)

            # if the specified identifier was not found raise error
            raise InvalidParameterValue('')

        return wps_response

outinputs = deque(maxlen=source.max_occurs)

        for inpt in inputs:
            data_input = source.clone()
            frmt = data_input.supported_formats[0]
            if 'mimeType' in inpt:
                if inpt['mimeType']:
                    frmt = data_input.get_format(inpt['mimeType'])
                else:
                    frmt = data_input.data_format

            if frmt:
                data_input.data_format = frmt
            else:
                raise InvalidParameterValue(
                    'Invalid mimeType value %s for input %s' %
                    (inpt.get('mimeType'), source.identifier),
                    'mimeType')

            data_input.method = inpt.get('method', 'GET')
            data_input.process(inpt)
            outinputs.append(data_input)

        if len(outinputs) < source.min_occurs:
            raise MissingParameterValue(description="Given data input is missing", locator=source.identifier)
        return outinputs

raise MissingParameterValue('', 'identifier')
        
        identifier_elements = []
        # 'all' keyword means all processes
        if 'all' in (ident.lower() for ident in identifiers):
            for process in self.processes:
                try:
                    identifier_elements.append(self.processes[process].describe_xml())
                except Exception as e:
                    raise NoApplicableCode(e)
        else:
            for identifier in identifiers:
                try:
                    process = self.processes[identifier]
                except KeyError:
                    raise InvalidParameterValue("Unknown process %r" % identifier, "identifier")
                else:
                    try:
                        identifier_elements.append(process.describe_xml())
                    except Exception as e:
                        raise NoApplicableCode(e)

        doc = WPS.ProcessDescriptions(
            *identifier_elements
        )
        doc.attrib['{http://www.w3.org/2001/XMLSchema-instance}schemaLocation'] = 'http://www.opengis.net/wps/1.0.0 http://schemas.opengis.net/wps/1.0.0/wpsDescribeProcess_response.xsd'
        doc.attrib['service'] = 'WPS'
        doc.attrib['version'] = '1.0.0'
        doc.attrib['{http://www.w3.org/XML/1998/namespace}lang'] = 'en-CA'
        return xml_response(doc)

self.outputs = get_output_from_xml(doc)
                self.raw = False
                if xpath_ns(doc, '/wps:Execute/wps:ResponseForm/wps:RawDataOutput'):
                    self.raw = True
                    # executeResponse XML will not be stored
                    self.store_execute = 'false'

                # check if response document tag has been set then retrieve
                response_document = xpath_ns(doc, './wps:ResponseForm/wps:ResponseDocument')
                if len(response_document) > 0:
                    self.lineage = response_document[0].attrib.get('lineage', 'false')
                    self.store_execute = response_document[0].attrib.get('storeExecuteResponse', 'false')
                    self.status = response_document[0].attrib.get('status', 'false')

            else:
                raise InvalidParameterValue(doc.tag)

        else:
            raise MethodNotAllowed()

def data_format(self, data_format):
        """self data_format setter
        """
        if self._is_supported(data_format):
            self._data_format = data_format
            if not data_format.validate or data_format.validate == emptyvalidator:
                data_format.validate = get_validator(data_format.mime_type)
        else:
            raise InvalidParameterValue("Requested format {}, {}, {} not supported".format(
                                        data_format.mime_type,
                                        data_format.encoding,
                                        data_format.schema),
                                        'mimeType')