Fix missing node

Author: wooorm

index.js

@@ -8,7 +8,10 @@ var digit6 = 54 // `6`
 
 // Rank of a heading: H1 -> 1, H2 -> 2, etc.
 function headingRank(node) {
-  var name = (node.type === 'element' ? node.tagName : '').toLowerCase()
+  var name = (
+    (node && node.type === 'element' && node.tagName) ||
+    ''
+  ).toLowerCase()
   var code =
     name.length === 2 && name.charCodeAt(0) === lowercaseH
       ? name.charCodeAt(1)

test.js

@@ -5,6 +5,8 @@ var h = require('hastscript')
 var rank = require('.')
 
 test('rank', function(t) {
+  t.equal(rank(), null, 'should return null for non-nodes')
+
   t.equal(
     rank({type: 'text', value: '!'}),
     null,