fix: metadata output breaks when common.css is output

packages/rollup/rollup.js

@@ -342,6 +342,10 @@ module.exports = (opts) => {
                 const meta = {};
 
                 out.forEach((value, entry) => {
+                    if(!bundle[entry]) {
+                        return;
+                    }
+
                     const { assets, dynamicAssets } = bundle[entry];
 
                     meta[entry] = {

packages/rollup/test/__snapshots__/splitting.test.js.snap

@@ -180,6 +180,57 @@ Array [
 ]
 `;
 
+exports[`/rollup.js code splitting should output metadata successfully when unreferenced CSS is output to common 1`] = `
+Array [
+  Object {
+    "file": "a.css",
+    "text": "/* packages/rollup/test/specimens/metadata/a.css */
+.mc541d3f5c_a { color: aqua; }
+",
+  },
+  Object {
+    "file": "b.css",
+    "text": "/* packages/rollup/test/specimens/metadata/b.css */
+.mc04101138_b { color: blue; }
+",
+  },
+  Object {
+    "file": "chunk.css",
+    "text": "/* packages/rollup/test/specimens/metadata/d.css */
+.mc7de0d66b_d { color: darkkhaki; }
+",
+  },
+  Object {
+    "file": "common.css",
+    "text": "/* fake.css */
+.mc2c838439_fake { color: red; }",
+  },
+  Object {
+    "file": "metadata.json",
+    "text": "{
+    \\"chunk2.js\\": {
+        \\"assets\\": [],
+        \\"dynamicAssets\\": [
+            \\"assets/chunk.css\\"
+        ]
+    },
+    \\"a.js\\": {
+        \\"assets\\": [
+            \\"assets/a.css\\"
+        ],
+        \\"dynamicAssets\\": []
+    },
+    \\"b.js\\": {
+        \\"assets\\": [
+            \\"assets/b.css\\"
+        ],
+        \\"dynamicAssets\\": []
+    }
+}",
+  },
+]
+`;
+
 exports[`/rollup.js code splitting should support circular JS dependencies 1`] = `
 Array [
   Object {

packages/rollup/test/splitting.test.js

@@ -5,6 +5,8 @@ const { rollup } = require("rollup");
 
 const shell = require("shelljs");
 
+const Processor = require("@modular-css/processor");
+
 const dir = require("@modular-css/test-utils/read-dir.js")(__dirname);
 const prefix = require("@modular-css/test-utils/prefix.js")(__dirname);
 const namer = require("@modular-css/test-utils/namer.js");
@@ -85,6 +87,40 @@ describe("/rollup.js", () => {
             expect(dir("./css-metadata/assets")).toMatchSnapshot();
         });
 
+        it("should output metadata successfully when unreferenced CSS is output to common", async () => {
+            const processor = new Processor();
+
+            await processor.string("./fake.css", ".fake { color: red; }");
+
+            const bundle = await rollup({
+                input : [
+                    require.resolve("./specimens/metadata/a.js"),
+                    require.resolve("./specimens/metadata/b.js"),
+                ],
+
+                plugins : [
+                    plugin({
+                        namer,
+                        map,
+                        processor,
+                        meta : true,
+                    }),
+                ],
+            });
+
+            await bundle.write({
+                format,
+                sourcemap,
+
+                assetFileNames,
+                chunkFileNames,
+
+                dir : prefix(`./output/css-metadata-common`),
+            });
+
+            expect(dir("./css-metadata-common/assets")).toMatchSnapshot();
+        });
+
         it("should support outputting metadata about CSS dependencies to a named file ", async () => {
             const bundle = await rollup({
                 input : [