rNMR @1.1.7: error: unable to start device X11

[ryandesign (Ryan Carsten Schmidt)]

​https://build.macports.org/builders/ports-11_x86_64-builder/builds/125645/steps/install-port/logs/stdio

* installing *source* package ‘rNMR’ ...
** using staged installation
** R
** inst
** byte-compile and prepare package for lazy loading
Warning message:
In fun(libname, pkgname) :
  no display name and no $DISPLAY environment variable
** help
*** installing help indices
** building package indices
** testing if installed package can be loaded from temporary location
Warning in fun(libname, pkgname) :
  no display name and no $DISPLAY environment variable
** testing if installed package can be loaded from final location
Warning in fun(libname, pkgname) :
  no display name and no $DISPLAY environment variable
Warning in X11(title = "Main Plot Window", width = defaultSettings$size.main[1],  :
  unable to open connection to X11 display ''
Error: package or namespace load failed for ‘rNMR’:
 .onLoad failed in loadNamespace() for 'rNMR', details:
  call: .External2(C_X11, d$display, d$width, d$height, d$pointsize, 
  error: unable to start device X11
Error: loading failed
Execution halted
ERROR: loading failed
* removing ‘/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_science_rNMR/rNMR/work/rNMR_1.1.7/pkg/rNMR’
Command failed: /opt/local/bin/R CMD INSTALL -l pkg --byte-compile --build /opt/local/var/macports/distfiles/rNMR/rNMR_1.1.7.tar.gz
Exit code: 1