fix empty example error. add lint rule.

Author: lavrton

lib/lint.js

@@ -34,6 +34,15 @@ function lintComments(comment) {
       }
     }
 
+    function checkEmptyExample(tag) {
+        if (!tag.description) {
+            comment.errors.push({
+              message: 'empty example is found',
+              commentLineNumber: tag.lineNumber
+            });
+        }
+    }
+
     function checkCanonical(type) {
       if (type.type === 'NameExpression') {
         nameInvariant(type.name);
@@ -51,6 +60,10 @@ function lintComments(comment) {
     if (tag.title === 'param' && tag.type) {
       checkCanonical(tag.type);
     }
+
+    if (tag.title === 'example') {
+      checkEmptyExample(tag);
+    }
   });
   return comment;
 }

lib/output/html.js

@@ -14,9 +14,9 @@ var walk = require('../walk'),
 function highlightString(auto) {
   return function (example) {
     if (auto) {
-      return hljs.highlightAuto(example).value;
+      return hljs.highlightAuto(example || '').value;
     }
-    return hljs.highlight('js', example).value;
+    return hljs.highlight('js', example || '').value;
   };
 }