@@ -11,7 +11,7 @@ let list = {
   },
 
   split(string, separators, last) {
-    if (!string) return []
+    if (typeof string !== 'string') return []
     let array = []
     let current = ''
     let split = false
 
@@ -36,6 +36,15 @@ test('comma() adds last empty', () => {
   equal(list.comma('a, b,'), ['a', 'b', ''])
 })
 
+test('comma() keeps empty value', () => {
+  equal(list.comma(''), [''])
+})
+
+test('comma() ignores non-string values', () => {
+  // @ts-expect-error Testing invalid API
+  equal(list.comma(undefined), [])
+})
+
 test('comma() checks quotes', () => {
   equal(list.comma('"a,b\\"", \'\''), ['"a,b\\""', "''"])
 })
 
@@ -13,6 +13,11 @@ test('returns array in selectors', () => {
   equal(rule.selectors, ['a', 'b'])
 })
 
+test('returns empty selector in selectors', () => {
+  let rule = new Rule({ selector: '' })
+  equal(rule.selectors, [''])
+})
+
 test('trims selectors', () => {
   let rule = new Rule({ selector: '.a\n, .b  , .c' })
   equal(rule.selectors, ['.a', '.b', '.c'])