install: further support for older npm versions

install.sh

@@ -152,10 +152,14 @@ nvm_check_global_modules() {
   NPM_VERSION="$(npm --version)"
   NPM_VERSION="${NPM_VERSION:--1}"
   [ "$NVM_DEBUG" = 0 ] && debug "NPM detected (at version ${NPM_VERSION}.)"
-  [ "${NPM_VERSION%%[!0-9]*}" -gt 0 ] || return 0
+  [ "${NPM_VERSION%%[!-0-9]*}" -gt 0 ] || return 0
 
   local NPM_GLOBAL_MODULES
-  NPM_GLOBAL_MODULES="$(npm list -g --depth=0 | sed '/ npm@/d')"
+  NPM_GLOBAL_MODULES="$(
+    npm list -g --depth=0 |
+    sed '/ npm@/d' |
+    sed '/ (empty)$/d'
+  )"
 
   local MODULE_COUNT
   MODULE_COUNT="$(