Convert null payloadCreator to the identity (#170)

Close #169

Author: yangmillstheory

README.md

@@ -24,7 +24,7 @@ import { createAction } from 'redux-actions';
 
 Wraps an action creator so that its return value is the payload of a Flux Standard Action. 
 
-`payloadCreator` must be a function or `undefined`. If `payloadCreator` is `undefined`, the identity function is used.
+`payloadCreator` must be a function, `undefined`, or `null`. If `payloadCreator` is `undefined` or `null`, the identity function is used.
 
 Example:
 

src/__tests__/createAction-test.js

@@ -23,16 +23,16 @@ describe('createAction()', () => {
       });
     });
 
-    it('should throw an error if payloadCreator is not a function or undefined', () => {
-      const wrongTypePayloadCreators = [1, false, null, 'string', {}, []];
+    it('should throw an error if payloadCreator is not a function, undefined, null', () => {
+      const wrongTypePayloadCreators = [1, false, 'string', {}, []];
 
       wrongTypePayloadCreators.forEach(wrongTypePayloadCreator => {
         expect(() => {
           createAction(type, wrongTypePayloadCreator);
         })
         .to.throw(
           Error,
-          'Expected payloadCreator to be a function or undefined'
+          'Expected payloadCreator to be a function, undefined or null'
         );
       });
     });
@@ -48,6 +48,17 @@ describe('createAction()', () => {
       expect(isFSA(action)).to.be.true;
     });
 
+    it('uses identity function if payloadCreator is null', () => {
+      const actionCreator = createAction(type, null);
+      const foobar = { foo: 'bar' };
+      const action = actionCreator(foobar);
+      expect(action).to.deep.equal({
+        type,
+        payload: foobar
+      });
+      expect(isFSA(action)).to.be.true;
+    });
+
     it('accepts a second parameter for adding meta to object', () => {
       const actionCreator = createAction(type, undefined, ({ cid }) => ({ cid }));
       const foobar = { foo: 'bar', cid: 5 };

src/createAction.js

@@ -1,22 +1,27 @@
 import identity from 'lodash/identity';
 import isFunction from 'lodash/isFunction';
 import isUndefined from 'lodash/isUndefined';
+import isNull from 'lodash/isNull';
 import invariant from 'invariant';
 
 export default function createAction(type, payloadCreator = identity, metaCreator) {
   invariant(
-    isFunction(payloadCreator),
-    'Expected payloadCreator to be a function or undefined'
+    isFunction(payloadCreator) || isNull(payloadCreator),
+    'Expected payloadCreator to be a function, undefined or null'
   );
 
+  const finalPayloadCreator = isNull(payloadCreator)
+    ? identity
+    : payloadCreator;
+
   const actionCreator = (...args) => {
     const hasError = args[0] instanceof Error;
 
     const action = {
       type
     };
 
-    const payload = hasError ? args[0] : payloadCreator(...args);
+    const payload = hasError ? args[0] : finalPayloadCreator(...args);
     if (!isUndefined(payload)) {
       action.payload = payload;
     }