diff --git a/src/createAction.js b/src/createAction.js
index 6a3f3042..5c39b419 100644
--- a/src/createAction.js
+++ b/src/createAction.js
@@ -1,7 +1,7 @@
 import invariant from 'invariant';
 import isFunction from './utils/isFunction';
 import identity from './utils/identity';
-import isNull from './utils/isNull';
+import isNil from './utils/isNil';
 
 export default function createAction(
   type,
@@ -9,18 +9,18 @@ export default function createAction(
   metaCreator
 ) {
   invariant(
-    isFunction(payloadCreator) || isNull(payloadCreator),
+    isFunction(payloadCreator) || isNil(payloadCreator),
     'Expected payloadCreator to be a function, undefined or null'
   );
 
   const finalPayloadCreator =
-    isNull(payloadCreator) || payloadCreator === identity
+    isNil(payloadCreator) || payloadCreator === identity
       ? identity
       : (head, ...args) =>
           head instanceof Error ? head : payloadCreator(head, ...args);
 
   const hasMeta = isFunction(metaCreator);
-  const typeString = type.toString();
+  const typeString = String(type);
 
   const actionCreator = (...args) => {
     const payload = finalPayloadCreator(...args);
diff --git a/src/utils/flattenWhenNode.js b/src/utils/flattenWhenNode.js
index 3ee137f1..9c23f61b 100644
--- a/src/utils/flattenWhenNode.js
+++ b/src/utils/flattenWhenNode.js
@@ -11,7 +11,7 @@ export default predicate =>
   ) {
     function connectNamespace(type) {
       if (!partialFlatActionType) return type;
-      const types = type.toString().split(ACTION_TYPE_DELIMITER);
+      const types = String(type).split(ACTION_TYPE_DELIMITER);
       const partials = partialFlatActionType.split(ACTION_TYPE_DELIMITER);
       return []
         .concat(...partials.map(p => types.map(t => `${p}${namespace}${t}`)))
diff --git a/src/utils/isNull.js b/src/utils/isNull.js
deleted file mode 100644
index b7664b39..00000000
--- a/src/utils/isNull.js
+++ /dev/null
@@ -1 +0,0 @@
-export default value => value === null;
diff --git a/src/utils/toString.js b/src/utils/toString.js
index e33f21a6..428d1cad 100644
--- a/src/utils/toString.js
+++ b/src/utils/toString.js
@@ -1 +1 @@
-export default value => value.toString();
+export default value => String(value);