refactor: normalize from var='' to var=""

shellcheck requires us putting '' or "" on the right-hand sides of
variable assignments unless `=' is at the end of line.  In the current
codebase, there are variations on var='' and var="", where most
instances are latter.  In this commit, I rewrite all var='' to match
the majority var="".

Author: akinomyoga

bash_completion

@@ -346,7 +346,7 @@ _comp_split()
 {
     local _assign='=' IFS=$' \t\n'
 
-    local OPTIND=1 OPTARG='' OPTERR=0 _opt
+    local OPTIND=1 OPTARG="" OPTERR=0 _opt
     while getopts ':alF:' _opt "$@"; do
         case $_opt in
             a) _assign='+=' ;;
@@ -936,7 +936,7 @@ _comp_initialize()
 {
     local exclude="" outx errx inx
 
-    local flag OPTIND=1 OPTARG='' OPTERR=0
+    local flag OPTIND=1 OPTARG="" OPTERR=0
     while getopts "n:e:o:i:s" flag "$@"; do
         case $flag in
             n) exclude+=$OPTARG ;;
@@ -2115,7 +2115,7 @@ _cd()
         return
     fi
 
-    local mark_dirs='' mark_symdirs=''
+    local mark_dirs="" mark_symdirs=""
     _comp_readline_variable_on mark-directories && mark_dirs=y
     _comp_readline_variable_on mark-symlinked-directories && mark_symdirs=y
 

completions/dpkg

@@ -13,7 +13,7 @@ if _comp_have_command grep-status; then
 else
     _comp_xfunc_dpkg_installed_packages()
     {
-        command awk -F '\n' -v RS='' "
+        command awk -F '\n' -v RS="" "
             index(\$1, \"Package: ${1-}\") == 1 &&
             \$2 ~ /ok installed|half-installed|unpacked|half-configured|^Essential: yes/ {
                 print(substr(\$1, 10));
@@ -22,7 +22,7 @@ else
 
     _comp_xfunc_dpkg_purgeable_packages()
     {
-        command awk -F '\n' -v RS='' "
+        command awk -F '\n' -v RS="" "
             index(\$1, \"Package: ${1-}\") == 1 &&
             \$2 ~ /ok installed|half-installed|unpacked|half-configured|config-files|^Essential: yes/ {
                 print(substr(\$1, 10));

test/t/unit/test_unit_variables.py

@@ -11,7 +11,7 @@ def functions(self, request, bash):
         assert_bash_exec(
             bash, "unset assoc2 && declare -A assoc2=([idx1]=1 [idx2]=2)"
         )
-        assert_bash_exec(bash, "unset ${!___v*} && declare ___var=''")
+        assert_bash_exec(bash, 'unset ${!___v*} && declare ___var=""')
         request.addfinalizer(
             lambda: assert_bash_exec(bash, "unset ___var assoc1 assoc2")
         )