Netlify build errors

Resently upgraded gatsby-plugin-robots-txt from 1.5.5 to 1.6.2 and I am getting this Netlify build error:

7:56:33 AM: error "gatsby-plugin-robots-txt" threw an error while running the onPostBuild lifecycle:
7:56:33 AM: Cannot read property 'startsWith' of null
7:56:33 AM:   78 |       new URL(mergedOptions.sitemap)
7:56:33 AM:   79 |     } catch {
7:56:33 AM: > 80 |       mergedOptions.sitemap = new URL(mergedOptions.sitemap.startsWith(pathPrefix) ? mergedOptions.sitemap : path.posix.join(pathPrefix, mergedOptions.sitemap), mergedOptions.host).toString()
7:56:33 AM:      |                                                             ^
7:56:33 AM:   81 |     }
7:56:33 AM:   82 |   }
7:56:33 AM:   83 |

My config is a one-to-one copy of the Netlify example in the docs. Went back to 1.5.6 and everything is fine. I’m assuming it has something to do with the changes in #441 and the docs just need to be updated with a new elimination.

[1-800-jono]

Latest merge was suppose to fix this but is not yet in npm. npm version still at 1.6.8

[ajmalafif]

@wildpow thanks for the step-by-step help for this!

~I think it‘s because I don‘t know how to do 2. Disabled Gatsby cache plug-in. which is why I think even though I‘m on 1.5.6 I still get the error~

edit: figured it out @wildpow thank you!