fix: safe checking if params are present for at rule (#871)

Author: Antonio-Laguna

src/plugins/postcss-icss-parser.js

@@ -75,8 +75,12 @@ export default postcss.plugin(
 
       // Replace tokens in at-rules
       css.walkAtRules((atrule) => {
-        // eslint-disable-next-line no-param-reassign
-        atrule.params = replaceImportsInString(atrule.params.toString());
+        // Due reusing `ast` from `postcss-loader` some plugins may lack
+        // `params` property, we need to account for this possibility
+        if (atrule.params) {
+          // eslint-disable-next-line no-param-reassign
+          atrule.params = replaceImportsInString(atrule.params.toString());
+        }
       });
 
       // Replace tokens in export