Fix empty urls (#1800)

src/printer.js

@@ -2741,7 +2741,8 @@ function genericPrintNoParens(path, options, print, args) {
       if (
         isURLCall &&
         (n.groups.length === 1 ||
-          (n.groups[0].type === "value-comma_group" &&
+          (n.groups.length > 0 &&
+            n.groups[0].type === "value-comma_group" &&
             n.groups[0].groups.length > 0 &&
             n.groups[0].groups[0].type === "value-word" &&
             n.groups[0].groups[0].value === "data"))

tests/css_inline_url/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,16 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`empty.css 1`] = `
+@font-face {
+  src: url();
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+@font-face  {
+  src: url();
+}
+
+`;
+
 exports[`inline_url.css 1`] = `
 .breadItem {
   background-image: url('/images/product/simple_product_manager/breadcrumb/chevron_right.png');

tests/css_inline_url/empty.css

@@ -0,0 +1,3 @@
+@font-face {
+  src: url();
+}