fix: fixed nested structure with text

Author: evless

example/stories/index.js

@@ -17,7 +17,7 @@ storiesOf('Basic', module)
   .add('flow', () => <SmartKnobedComponentWithFlow />)
   .add('nested example', () => (
     <div>
-      <span />
+      <h1>Title</h1>
       <SmartKnobedComponent />
     </div>
   ))

src/index.js

@@ -97,13 +97,13 @@ const getNewProps = (target, context) => {
 
 const mutateChildren = (component) => {
   return cloneElement(component, { children: Children.map(component.props.children, (child) => {
-    if (child.type.__docgenInfo) {
+    if (child.type && child.type.__docgenInfo) {
       const newProps = getNewProps(child)
 
       return cloneElement(child, { ...child.props, ...newProps })
     }
 
-    if (child.props.children) {
+    if (child.props && child.props.children) {
       return mutateChildren(child)
     }