check existence of dirs before reading them in file tracking logic (#150)

Author: lindsaylevine

lib/helpers/handleFileTracking.js

@@ -56,12 +56,14 @@ const handleFileTracking = ({ functionsPath, publishPath }) => {
 
   // this callback will run at the end of nextOnNetlify()
   const trackNewFiles = () => {
-    const functionsAfterRun = isConfiguredFunctionsDir
-      ? readdirSync(functionsPath)
-      : functionsBeforeRun;
-    const publishAfterRun = isConfiguredPublishDir
-      ? readdirSync(publishPath)
-      : publishBeforeRun;
+    const functionsAfterRun =
+      isConfiguredFunctionsDir && existsSync(functionsPath)
+        ? readdirSync(functionsPath)
+        : functionsBeforeRun;
+    const publishAfterRun =
+      isConfiguredPublishDir && existsSync(publishPath)
+        ? readdirSync(publishPath)
+        : publishBeforeRun;
     const getDifference = (before, after) =>
       after.filter((filePath) => !before.includes(filePath));
     const newFunctionsFiles = getDifference(