fix: fix crash when source map is unavailable with external URL in @import

Author: cap-Bernardito

src/runtime/cssWithMappingToString.js

@@ -1,6 +1,10 @@
 module.exports = function cssWithMappingToString(item) {
   const [, content, , cssMapping] = item;
 
+  if (!cssMapping) {
+    return content;
+  }
+
   if (typeof btoa === "function") {
     // eslint-disable-next-line no-undef
     const base64 = btoa(

test/runtime/__snapshots__/api.test.js.snap

@@ -18,6 +18,8 @@ exports[`api should toString with a source map without "sourceRoot" 1`] = `
 /*# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJmaWxlIjoidGVzdC5zY3NzIiwic291cmNlcyI6WyIuL3BhdGgvdG8vdGVzdC5zY3NzIl0sIm1hcHBpbmdzIjoiQUFBQTsifQ== */"
 `;
 
+exports[`api should toString with a source map without map 1`] = `"@import url('https://fonts.googleapis.com/css?family=Open+Sans&display=swap');"`;
+
 exports[`api should toString with media query 1`] = `"body { b: 2; }body { c: 3; }body { b: 2; }@media print {body { b: 2; }}@media print {body { d: 4; }}@media screen {body { a: 1; }}"`;
 
 exports[`api should toString with source mapping 1`] = `

test/runtime/api.test.js

@@ -145,6 +145,18 @@ describe("api", () => {
     expect(m.toString()).toMatchSnapshot();
   });
 
+  // https://github.com/webpack-contrib/css-loader/issues/1322
+  it("should toString with a source map without map", () => {
+    const m = api(cssWithMappingToString);
+
+    m.push([
+      1,
+      "@import url('https://fonts.googleapis.com/css?family=Open+Sans&display=swap');",
+    ]);
+
+    expect(m.toString()).toMatchSnapshot();
+  });
+
   it("should import modules with dedupe", () => {
     const m = api((i) => i[1]);
 

test/sourceMap-option.test.js

@@ -501,8 +501,8 @@ describe('"sourceMap" option', () => {
 
       expect(chunkName).toBe(
         webpack.version[0] === "5"
-          ? "main.6480a869998e0b381c90.bundle.js"
-          : "main.19efc497c5c37fc5e355.bundle.js"
+          ? "main.b67984bbf9dd298785fb.bundle.js"
+          : "main.a64c858ed0f4c1ed322c.bundle.js"
       );
       expect(
         getModuleSource("fixtures/source-map/basic.css", stats)