This is a buffer here

Author: GeoffreyBooth

lib/internal/modules/esm/get_format.js

@@ -84,16 +84,13 @@ function underNodeModules(url) {
 
 /**
  * Determine whether the given source contains CJS or ESM module syntax.
- * @param {string} source
+ * @param {string | Buffer | undefined} source
  * @param {URL} url
  */
 function detectModuleFormat(source, url) {
-  try {
-    return containsModuleSyntax(source, fileURLToPath(url), url) ? 'module' : 'commonjs';
-  } catch {
-    // containsModuleSyntax throws if source is undefined and the passed filename cannot be read
-    // Return undefined so that the load hook can determine the format
-  }
+  const moduleSource = source ? `${source}` : undefined;
+  const modulePath = fileURLToPath(url);
+  return containsModuleSyntax(moduleSource, modulePath, url) ? 'module' : 'commonjs'
 }
 
 let typelessPackageJsonFilesWarnedAbout;