return nil instread of 0 in uncached_version when Xcode/CLT are not present, to distinguish from linuxbrew behavior
return nil instread of 0 in uncached_version when Xcode/CLT are not present, to distinguish from linuxbrew behavior

woodruffw/homebrew-test,woodruffw/homebrew-test,woodruffw/homebrew-test,woodruffw/homebrew-test