handle error for src folders while using tags (#3824)

lib/runner/folder-walk.js

@@ -68,12 +68,12 @@ class Walker {
       err.showTrace = false;
 
       if (Array.isArray(this.settings.src_folders) && this.settings.src_folders.length > 0) {
-        let srcFolders = this.settings.src_folders.map(item => `"${item}"`).join(', ');
+        const srcFolders = this.settings.src_folders.map(item => `"${item}"`).join(', ');
         err.message += `; src_folders: ${srcFolders}`;
       }
 
       if (this.argv.group) {
-        let groups = this.argv.group.map(item => `"${item}"`).join(', ');
+        const groups = this.argv.group.map(item => `"${item}"`).join(', ');
         err.message += `; group(s): ${groups}`;
       }
 
@@ -118,7 +118,7 @@ class Walker {
         matched = false;
       }
 
-      let filename = filePath.split(path.sep).slice(-1)[0];
+      const filename = filePath.split(path.sep).slice(-1)[0];
 
       if (this.settings.filename_filter) {
         matched = matched && minimatch(filename, this.settings.filename_filter);
@@ -129,6 +129,10 @@ class Walker {
   }
 
   async applyTagFilter(list) {
+    if (!Array.isArray(list)) {
+      return;
+    }
+
     if (!this.tags.anyTagsDefined() || this.usingCucumber) {
       return list;
     }
@@ -147,7 +151,7 @@ class Walker {
   }
 
   promiseFn(resolve, reject) {
-    let sourcePath = this.modulePathsCopy.shift();
+    const sourcePath = this.modulePathsCopy.shift();
     let fullPath = path.resolve(sourcePath);
 
     Utils.checkPath(fullPath)