Change: Use the absence of "field" to refer to the root of customapi response

docs/widgets/services/customapi.md

@@ -57,8 +57,8 @@ widget:
     - field: key
       label: Number of things in array
       format: size
-    - field: . # This will take the root of the API response, e.g. when APIs return an array
-      label: Number of items
+    # This (no field) will take the root of the API response, e.g. when APIs return an array:
+    - label: Number of items
       format: size
 ```
 

src/widgets/customapi/component.jsx

@@ -20,7 +20,7 @@ function getValue(field, data) {
   let key = "";
 
   // Support APIs that return arrays or scalars directly.
-  if (field === ".") {
+  if (typeof field === "undefined") {
     return value;
   }