test and implementation for empty collections

lib/index.js

@@ -40,6 +40,14 @@ function plugin(opts){
       });
     });
 
+    /**
+     * Ensure that a default empty collection exists.
+     */
+
+    keys.forEach(function(key) {
+      metadata[key] = metadata[key] || [];
+    });
+
     /**
      * Sort the collections.
      */
@@ -139,4 +147,4 @@ function matcher(cols){
     }
     return unique(matches);
   };
-}
+}

test/fixtures/basic/build/one.md

@@ -1 +1,2 @@
+
 one

test/fixtures/basic/build/two.md

@@ -1 +1,2 @@
+
 two

test/fixtures/empty/build/one.md

@@ -0,0 +1,2 @@
+
+one

test/fixtures/empty/src/one.md

@@ -0,0 +1,5 @@
+---
+title: No collection here
+---
+
+one

test/fixtures/pattern/build/one.md

@@ -1 +1,2 @@
+
 one

test/fixtures/pattern/build/two.md

@@ -1 +1,2 @@
+
 two

test/fixtures/references/build/one.md

@@ -1 +1,2 @@
+
 one

test/fixtures/references/build/three.md

@@ -1 +1,2 @@
+
 three

test/fixtures/references/build/two.md

@@ -1 +1,2 @@
+
 two

test/fixtures/sort/build/one.md

@@ -1 +1,2 @@
+
 one

test/fixtures/sort/build/three.md

@@ -1 +1,2 @@
+
 three

test/fixtures/sort/build/two.md

@@ -1 +1,2 @@
+
 two

test/index.js

@@ -128,4 +128,21 @@ describe('metalsmith-collections', function(){
         done();
       });
   });
-});
+
+  it('should not fail with empty collections', function(done) {
+    var metalsmith = Metalsmith('test/fixtures/empty');
+    metalsmith
+      .use(collections({
+        articles: {
+          sortBy: 'date',
+          reverse: true
+        }
+      }))
+      .build(function(err) {
+        if (err) return done(err);
+        var articles = metalsmith.metadata().articles;
+        assert.equal(articles.length, 0);
+        done();
+      });
+  });
+});