Path must be a string. Received undefined

[gergely-xyz]

Both activate license and build fail with this error. I don't know what "Path" might be undefined

2020-05-14T14:47:27.6791685Z ##[section]Starting: Unity Build standalone
2020-05-14T14:47:27.6940130Z ==============================================================================
2020-05-14T14:47:27.6940510Z Task         : Unity Build
2020-05-14T14:47:27.6940834Z Description  : Build a Unity project and get the exported output files.
2020-05-14T14:47:27.6941100Z Version      : 3.1.1
2020-05-14T14:47:27.6941325Z Author       : Dinomite Studios
2020-05-14T14:47:27.6941754Z Help         : Builds a Unity project to supported build target platforms. [More Information](https://github.com/Dinomite-Studios/unity-azure-pipelines-tasks)
2020-05-14T14:47:27.6942192Z ==============================================================================
2020-05-14T14:47:27.9708314Z Determining Unity editor version for project at C:\agent\_work\r1\a\Source
2020-05-14T14:47:27.9742474Z Success, Unity editor version found 2019.3.13f1, alpha=false, beta=false
2020-05-14T14:47:27.9755441Z Path must be a string. Received undefined
2020-05-14T14:47:27.9789058Z ##[error]Path must be a string. Received undefined
2020-05-14T14:47:27.9813879Z ##[section]Finishing: Unity Build standalone