Test utilities can be added without specifying variants

__tests__/processPlugins.test.js

@@ -314,3 +314,25 @@ test('the "@" sign is optional in at-rules', () => {
     }
   `)
 })
+
+test('variants are optional when adding utilities', () => {
+  const [components, utilities] = processPlugins({
+    plugins: [
+      function ({ rule, addUtilities }) {
+        addUtilities([
+          rule('.border-collapse', {
+            'border-collapse': 'collapse'
+          })
+        ])
+      }
+    ],
+  })
+
+  expect(css(utilities)).toMatchCss(`
+    @variants {
+      .border-collapse {
+        border-collapse: collapse
+      }
+    }
+  `)
+})

src/util/processPlugins.js

@@ -35,7 +35,7 @@ export default function(config) {
       rule: defineRule,
       atRule: defineAtRule,
       e: escapeClassName,
-      addUtilities: (utilities, variants) => {
+      addUtilities: (utilities, variants = []) => {
         pluginUtilities.push(wrapWithVariants(utilities, variants))
       },
       addComponents: components => {