fix: catch err internally when getItemData doesnt find any (#505)

AFFECTS PACKAGES:
@esri/arcgis-rest-items

ISSUES CLOSED: #504

packages/arcgis-rest-items/src/get.ts

@@ -55,7 +55,7 @@ export function getItem(
  * getItemData("ae7", { authentication })
  *   .then(response)
  * ```
- * Get the /data for an item. See the [REST Documentation](https://developers.arcgis.com/rest/users-groups-and-items/item-data.htm) for more information.
+ * Get the /data for an item. If no data exists, returns `undefined`. See the [REST Documentation](https://developers.arcgis.com/rest/users-groups-and-items/item-data.htm) for more information.
  * @param id - Item Id
  * @param requestOptions - Options for the request
  * @returns A Promise that will resolve with the json data for the item.
@@ -75,7 +75,17 @@ export function getItemData(
     options.params.f = null;
   }
 
-  return request(url, options);
+  return request(url, options).catch(err => {
+    /* if the item doesn't include data, the response will be empty
+       and the internal call to response.json() will fail */
+    const emptyResponseErr = RegExp(
+      /Unexpected end of (JSON input|data at line 1 column 1)/i
+    );
+    /* istanbul ignore else */
+    if (emptyResponseErr.test(err.message)) {
+      return;
+    } else throw err;
+  });
 }
 
 export interface IGetRelatedItemsResponse {

packages/arcgis-rest-items/test/get.test.ts

@@ -30,7 +30,7 @@ describe("get", () => {
     fetchMock.once("*", ItemResponse);
 
     getItem("3ef")
-      .then(response => {
+      .then(() => {
         expect(fetchMock.called()).toEqual(true);
         const [url, options]: [string, RequestInit] = fetchMock.lastCall("*");
         expect(url).toEqual(
@@ -90,6 +90,29 @@ describe("get", () => {
     }
   });
 
+  it("should return a valid response even when no data is retrieved", done => {
+    fetchMock.once("*", {
+      sendAsJson: false,
+      headers: { "Content-Type": "text/plain;charset=utf-8" },
+      body: ""
+    });
+
+    getItemData("3ef")
+      .then(response => {
+        expect(fetchMock.called()).toEqual(true);
+        const [url, options]: [string, RequestInit] = fetchMock.lastCall("*");
+        expect(url).toEqual(
+          "https://www.arcgis.com/sharing/rest/content/items/3ef/data?f=json"
+        );
+        expect(options.method).toBe("GET");
+        expect(response).toBe(undefined);
+        done();
+      })
+      .catch(e => {
+        fail(e);
+      });
+  });
+
   it("should return related items", done => {
     fetchMock.once("*", RelatedItemsResponse);