Minor tweaks to functions

public/js/appChart.js

@@ -125,6 +125,7 @@ export const PARAM_SELECT = "result,phenomenonTime";
  * @returns {Array} Array of formatted observations suitable for use in a heatmap
  */
 export const formatSTAResponseForHeatMap = function (obsArray) {
+  if (!obsArray) return;
   const dataSTAFormatted = [];
   obsArray.forEach((obs) => {
     // Get the date/time string; first element in input array; remove trailing "Z"
@@ -246,6 +247,7 @@ export const drawHeatMapHC = function (formattedObsArrayForHeatmap) {
  * @returns {Array} Array of formatted observations suitable for use in a line chart
  */
 export const formatSTAResponseForLineChart = function (obsArray) {
+  if (!obsArray) return;
   const dataSTAFormatted = [];
   obsArray.forEach((result) => {
     const timestampObs = new Date(result[0].slice(0, -1)).getTime(); // slice() removes trailing "Z" character in timestamp
@@ -302,6 +304,7 @@ export const drawLineChartHC = function (formattedObsArrayForLineChart) {
  * @returns {Object} - Object containing results from all the "@iot.nextLink" links
  */
 export const followNextLink = function (responsePromise) {
+  if (!responsePromise) return;
   return responsePromise
     .then(function (lastSuccess) {
       if (lastSuccess.data["@iot.nextLink"]) {