work with node 12

Author: ryndh

lib/lockfileV1/tree.js

@@ -21,7 +21,7 @@ const {
 
 module.exports = {
   buildYarnTree (nodeModulesTree, packageLock) {
-    const flattenedPackageLock = flattenPackageLock(packageLock.dependencies ?? packageLock.packages)
+    const flattenedPackageLock = flattenPackageLock(packageLock.dependencies || packageLock.packages)
     const tree = Object.keys(nodeModulesTree).reduce((tree, path) => {
       const nmEntry = nodeModulesTree[path]
       const { name } = nmEntry