UnhandledPromiseRejectionWarning: TypeError: Cannot convert undefined or null to object code example
Example: TypeError: Cannot convert undefined or null to object at Function.values () in solidity
I had this issue when compiling using my global truffle module. i switched to npx truffle compile after installing it as a dev dependency. The global module was v5.0.5 and the local module was v5.2.6 . so you might want to check your compiler version.