Buidler fails on api initialization

[maxsam4]

Since I upgraded builder to version 1.3.0-rc.0, coverage has stopped working with the following error:
Error BDLR301: Invalid value null for argument testfiles of type string

Seems like buidler no longer accepts null values for --testfiles, --solcoverjs and --temp which seems to be the default ones used by solidity-coverage.

[cgewecke]

@maxsam4 Thanks for reporting. What was the last buidler version you were using that worked?

[jjgonecrypto]

It worked on 1.2.0

[cgewecke]

@maxsam4 Fixed this in #490, will publish this am...

[cgewecke]

Should be resolved in 0.7.3, please just ping if you're still seeing any problems with the cli options (or any other Buidler stuff)