fix(fela-plugin-extend): don't throw on undefined items in extend array

packages/fela-plugin-extend/src/__tests__/extend-test.js

@@ -156,6 +156,18 @@ describe('Extend plugin', () => {
     })
   })
 
+  it('should filter out null items in extend array', () => {
+    const base = {
+      color: 'blue',
+      extend: [{ backgroundColor: '#ccc' }, null],
+    }
+
+    expect(extend()(base)).toEqual({
+      color: 'blue',
+      backgroundColor: '#ccc',
+    })
+  })
+
   it('should not overwrite values with null or undefined', () => {
     const base = {
       color: 'blue',

packages/fela-plugin-extend/src/index.js

@@ -22,7 +22,10 @@ function removeUndefined(style: Object): Object {
 
 function extendStyle(style: Object, extension: Object): void {
   // extend conditional style objects
-  if (extension.hasOwnProperty('condition')) {
+  if (
+    extension &&
+    Object.prototype.hasOwnProperty.call(extension, 'condition')
+  ) {
     if (extension.condition) {
       // eslint-disable-next-line no-use-before-define
       assignStyle(style, extend(extension.style))