Handle undefined props like className (#564)

.github/workflows/ci.yml

@@ -10,17 +10,9 @@ jobs:
       matrix:
         node: [14]
         react: [
-          16.3.x,
-          16.4.x,
-          16.5.x,
-          16.6.x,
-          16.7.x,
-          16.8.x,
-          16.9.x,
-          16.10.x,
-          16.11.x,
-          16.12.x,
-          17.0.x
+          16.x,
+          17.x,
+          18.x
         ]
         fontawesome-svg-core: [
           1.2.x,

src/components/FontAwesomeIcon.js

@@ -53,7 +53,7 @@ const FontAwesomeIcon = React.forwardRef((props, ref) => {
 
   const classes = objectWithKey('classes', [
     ...classList(allProps),
-    ...className.split(' ')
+    ...(className || '').split(' ')
   ])
   const transform = objectWithKey(
     'transform',

src/components/__tests__/FontAwesomeIcon.test.js

@@ -73,6 +73,42 @@ if (coreHasFeature(REFERENCE_ICON_BY_STYLE)) {
   })
 }
 
+describe.only('using defaultProps', () => {
+  const UNDEFINED_DEFAULT_PROPS = {
+    border: undefined,
+    className: undefined,
+    mask: undefined,
+    maskId: undefined,
+    fixedWidth: undefined,
+    inverse: undefined,
+    flip: undefined,
+    listItem: undefined,
+    pull: undefined,
+    pulse: undefined,
+    rotation: undefined,
+    size: undefined,
+    spin: undefined,
+    spinPulse: undefined,
+    spinReverse: undefined,
+    beat: undefined,
+    fade: undefined,
+    beatFade: undefined,
+    bounce: undefined,
+    shake: undefined,
+    symbol: undefined,
+    title: undefined,
+    titleId: undefined,
+    transform: undefined,
+    swapOpacity: undefined
+  }
+
+  test('undefined props passed', () => {
+    expect(() =>
+      mount({ icon: faCoffee, ...UNDEFINED_DEFAULT_PROPS })
+    ).not.toThrow(TypeError)
+  })
+})
+
 test('using imported object from svg icons package', () => {
   const vm = mount({
     icon: faTimes