docs(gatsby-source-filesystem): add warning about parentNodeId for util functions

Author: georgiee

packages/gatsby-source-filesystem/README.md

@@ -166,7 +166,6 @@ While downloading the assets, special characters (regex: `/:|\/|\*|\?|"|<|>|\||\
 
 **Warning**: Please make sure to pass in the `parentNodeId`. Otherwise if the parent of the created file node is loaded from the cache, the linked file node won't be recreated which means it will be garbage collected and your file is set to null.
 
-
 ```javascript
 createRemoteFileNode({
   // The source url of the remote file
@@ -268,72 +267,70 @@ The `createFileNodeFromBuffer` helper accepts a `Buffer`, caches its contents to
 
 **Warning**: Please make sure to pass in the `parentNodeId`. Otherwise if the parent of the created file node is loaded from the cache, the linked file node won't be recreated which means it will be garbage collected and your file is set to null.
 
-
 #### Example usage
 
 The following example is a common case where you want to create a sharing image dynamically, instead of loading an existing image.
 
 ```js
 // gatsby-node.js
 exports.onCreateNode = async ({ node, actions, getCache, createNodeId }) => {
-  const { createNode, createNodeField } = actions;
+  const { createNode, createNodeField } = actions
   /**
    * For every incoming Markdown node we want to generate a social card
    * and attach it to the the node.
    */
-  if (node.internal.type === 'MarkdownRemark') {
-    const title = node.frontmatter.title;
+  if (node.internal.type === "MarkdownRemark") {
+    const title = node.frontmatter.title
     // we need the title in order to generate anything
     if (!title) {
-      return;
+      return
     }
 
     // this some function that generates your image as a buffer
     // use `node-canvas` (https://www.npmjs.com/package/canvas) or similar.
-    const imageBuffer = await generateSomeImage(title);
+    const imageBuffer = await generateSomeImage(title)
 
     const fileNode = await createFileNodeFromBuffer({
-      name: 'social-card',
+      name: "social-card",
       buffer: imageBuffer,
       getCache,
       createNode,
       createNodeId,
       // make sure to always pass in the parent node otherwise it's lost when loaded from cache
-      parentNodeId: node.id 
-    });
+      parentNodeId: node.id,
+    })
 
     if (fileNode) {
       createNodeField({
         node,
         name: `socialCard`,
         value: fileNode.id,
-      });
+      })
     }
   }
-};
-
+}
 
-exports.createSchemaCustomization = ({ actions: { createTypes }}) => {
+exports.createSchemaCustomization = ({ actions: { createTypes } }) => {
   const typeDefs = [
-    `type SyPersonioJob implements Node { 
+    `type MarkdownRemark implements Node { 
       socialCardFile: File @link(from: "fields.socialCard")
     }`,
-  ];
-
-  createTypes(typeDefs);
-};
+  ]
 
+  createTypes(typeDefs)
+}
 ```
 
 ## Troubleshooting
 
 ### File nodes are null after starting the server a second time
- In case you see yourself running `gatsby clean` frequently to files that are set to `null` you might might have forgotten to pass in `parentNodeId` to `createFileNodeFromBuffer` or `createRemoteFileNode`. Make sure you always provide a parent reference otherwise the files won't be recreated which means it will be garbage collected and show up as `null` in your queried data.
+
+In case you see yourself running `gatsby clean` frequently to files that are set to `null` you might might have forgotten to pass in `parentNodeId` to `createFileNodeFromBuffer` or `createRemoteFileNode`. Make sure you always provide a parent reference otherwise the files won't be recreated which means it will be garbage collected and show up as `null` in your queried data.
 
 ### Spotty network
+
 In case that due to spotty network, or slow connection, some remote files fail to download. Even after multiple retries and adjusting concurrent downloads, you can adjust timeout and retry settings with these environment variables:
 
 - `GATSBY_STALL_RETRY_LIMIT`, default: `3`
 - `GATSBY_STALL_TIMEOUT`, default: `30000`
 - `GATSBY_CONNECTION_TIMEOUT`, default: `30000`
-

packages/gatsby-source-filesystem/src/create-file-node-from-buffer.js

@@ -148,9 +148,10 @@ module.exports = ({
     )
   }
 
-
-  if (typeof parentNodeId === null) {
-    console.warn(`It seems that you forgot to pass in 'parentNodeId' for a file you try to create with 'create-file-node-from-buffer'. Not doing this is causing problems as a) when the server is restarted, if the parent of the created file node is loaded from the cache, the linked file node won't be recreated which means it will be garbage collected and b) if a parent node is deleted, the linked file node won't also be deleted.`)
+  if (parentNodeId === null) {
+    console.warn(
+      `It seems that you forgot to pass in 'parentNodeId' for a file you try to create with 'createFileNodeFromBuffer'. Not doing this is causing problems as a) when the server is restarted, if the parent of the created file node is loaded from the cache, the linked file node won't be recreated which means it will be garbage collected and b) if a parent node is deleted, the linked file node won't also be deleted.`
+    )
   }
 
   if (!buffer) {

packages/gatsby-source-filesystem/src/create-remote-file-node.js

@@ -237,8 +237,10 @@ module.exports = function createRemoteFileNode({
     )
   }
 
-  if (typeof parentNodeId === null) {
-    console.warn(`It seems that you forgot to pass in 'parentNodeId' for a file you try to create with 'create-remote-file-node'. Not doing this is causing problems as a) when the server is restarted, if the parent of the created file node is loaded from the cache, the linked file node won't be recreated which means it will be garbage collected and b) if a parent node is deleted, the linked File node won't also be deleted.`)
+  if (parentNodeId === null) {
+    console.warn(
+      `It seems that you forgot to pass in 'parentNodeId' for a file you try to create with 'createRemoteFileNode'. Not doing this is causing problems as a) when the server is restarted, if the parent of the created file node is loaded from the cache, the linked file node won't be recreated which means it will be garbage collected and b) if a parent node is deleted, the linked File node won't also be deleted.`
+    )
   }
 
   // Check if we already requested node for this remote file