snapshot() computing Rd index failed:cannot open the connection

snapshot() produces the following error, not really sure what to make of the output, where should 'man' exist, why doesn't it....etc. Thanks for any help.

Fetching sources for brew (1.0-6) ... Fetching sources for cli (1.1.0) ... Fetching sources for clisymbols (1.2.0) ... Fetching sources for commonmark (1.7) ... Fetching sources for covr (3.3.2) ... Fetching sources for desc (1.2.0) ... Fetching sources for fs (1.3.1) ... Fetching sources for gh (1.0.1) ... Fetching sources for git2r (0.24.0) ... Fetching sources for ini (0.3.1) ... Fetching sources for memoise (1.1.0) ... Fetching sources for pkgbuild (1.0.6) ... Fetching sources for pkgload (1.0.2) ... Fetching sources for praise (1.0.0) ... Fetching sources for rcmdcheck (1.3.3) ... Fetching sources for remotes (2.1.0) ... Fetching sources for rex (1.1.2) ... Fetching sources for rprojroot (1.3-2) ... Fetching sources for rstudioapi (0.9.0) ... Fetching sources for rversions (2.0.0) ... Fetching sources for sessioninfo (1.1.1) ... Fetching sources for testthat (2.3.0) ... Fetching sources for usethis (1.5.1) ... Fetching sources for xml2 (1.2.0) ... Fetching sources for xopen (1.0.0) ... Error in snapshotSources(project, activeRepos(project), allRecordsFlat) :
Errors occurred when fetching source files:
Error : Command failed (1)

Failed to run system command:

'/Library/Frameworks/R.framework/Resources/bin/R' --vanilla CMD build '/Library/Frameworks/R.framework/Versions/3.5/Resources/library/brew' --no-manual --no-resave-data --no-build-vignettes

The command failed with output:

• checking for file '/Library/Frameworks/R.framework/Versions/3.5/Resources/library/brew/DESCRIPTION' ... OK
• preparing 'brew':
• checking DESCRIPTION meta-information ... OK
  Warning in file(con, "r") :
  cannot open file 'man': No such file or directory
  ERROR
  computing Rd index failed:cannot open the connection
  Error : Command failed (1)

Failed to run system command:

'/Library/Frameworks/R.framework/Resources/bin/R' --vanilla CMD build '/Users/clab683/Library/R/3.5/library/cli' --no-manual --no-resave-data --no-build-vignettes

The command failed with output:

• checking for file '/Users/clab683/Library/R/3.5/library/cli/DESCRIPTION' ... OK
• prepari

R version 3.5.2 (2018-12-20)
Platform: x86_64-apple-darwin15.6.0 (64-bit)
Running under: macOS Mojave 10.14.6

local libPaths: "/Users/clab683/Library/R/3.5/library" "/Library/Frameworks/R.framework/Versions/3.5/Resources/library"

packrat 0.5.0

The failure is reported in snapshotSources while running R CMD build on installed packages such as brew and cli. Start by reproducing the command under R 3.5.2 on macOS and inspect the package sources around the missing man path; done means identifying a reproducible cause and documenting or fixing it with a regression test.