fix(arborist): safeguard against null node.target in flag calculation

workspaces/arborist/lib/calc-dep-flags.js

@@ -31,6 +31,10 @@ const calcDepFlagsStep = (node) => {
 
   // for links, map their hierarchy appropriately
   if (node.isLink) {
+    // node.target can be null, we check to ensure it's not null before proceeding
+    if (node.target == null) {
+      return node
+    }
     node.target.dev = node.dev
     node.target.optional = node.optional
     node.target.devOptional = node.devOptional
@@ -97,15 +101,18 @@ const unsetFlag = (node, flag) => {
       tree: node,
       visit: node => {
         node.extraneous = node[flag] = false
-        if (node.isLink) {
+        if (node.isLink && node.target) {
           node.target.extraneous = node.target[flag] = false
         }
       },
       getChildren: node => {
         const children = []
-        for (const edge of node.target.edgesOut.values()) {
-          if (edge.to && edge.to[flag] &&
-            (flag !== 'peer' && edge.type === 'peer' || edge.type === 'prod')
+        const targetNode = node.isLink && node.target ? node.target : node
+        for (const edge of targetNode.edgesOut.values()) {
+          if (
+            edge.to &&
+            edge.to[flag] &&
+            ((flag !== 'peer' && edge.type === 'peer') || edge.type === 'prod')
           ) {
             children.push(edge.to)
           }

workspaces/arborist/test/calc-dep-flags.js

@@ -264,3 +264,16 @@ t.test('set parents to not extraneous when visiting', t => {
   t.equal(bazLink.devOptional, false, 'bazlink not devOptional')
   t.end()
 })
+
+t.test('check null target in link', async t => {
+  const root = new Link({
+    path: '/some/path',
+    realpath: '/some/path',
+    pkg: {
+      dependencies: { foo: '' },
+    },
+  })
+  t.doesNotThrow(() => calcDepFlags(root))
+  t.doesNotThrow(() => calcDepFlags(root, false))
+  t.end()
+})