diff --git a/themes/essential/essential.theme.bash b/themes/essential/essential.theme.bash
old mode 100644
new mode 100755
index ae988733cd..dbf17e97b7
--- a/themes/essential/essential.theme.bash
+++ b/themes/essential/essential.theme.bash
@@ -1,42 +1,41 @@
 #!/usr/bin/env bash
 
 # https://github.com/koalaman/shellcheck/wiki/Sc2154
-# shellcheck disable=SC2154
 
 function _user-prompt() {
   local -r user='\\u'
 
   if [[ "${EUID}" -eq 0 ]]; then
     # Privileged users:
-    local -r user_color="${bold_red}"
+    local -r user_color="${bold_red?}"
   else
     # Standard users:
-    local -r user_color="${bold_green}"
+    local -r user_color="${bold_green?}"
   fi
 
   # Print the current user's name (colored according to their current EUID):
-  echo -e "${user_color}${user}${normal}"
+  echo -e "${user_color}${user}${normal?}"
 }
 
 function _host-prompt() {
   local -r host='\\h'
 
   # Check whether or not $SSH_TTY is set:
-  if [[ -z "${SSH_TTY}" ]]; then
+  if [[ -z "${SSH_TTY:-}" ]]; then
     # For local hosts, set the host's prompt color to blue:
-    local -r host_color="${bold_blue}"
+    local -r host_color="${bold_blue?}"
   else
     # For remote hosts, set the host's prompt color to red:
-    local -r host_color="${bold_red}"
+    local -r host_color="${bold_red?}"
   fi
 
   # Print the current hostname (colored according to $SSH_TTY's status):
-  echo -e "${host_color}${host}${normal}"
+  echo -e "${host_color}${host}${normal?}"
 }
 
 function _user-at-host-prompt() {
   # Concatenate the user and host prompts into: user@host:
-  echo -e "$(_user-prompt)${bold_white}@$(_host-prompt)"
+  echo -e "$(_user-prompt)${bold_white?}@$(_host-prompt)"
 }
 
 function _exit-status-prompt() {
@@ -47,32 +46,32 @@ function _exit-status-prompt() {
   if [[ "${exit_status}" -eq 0 ]]; then
     # For commands that return an exit status of zero, set the exit status's
     # notifier to green:
-    local -r exit_status_color="${bold_green}"
+    local -r exit_status_color="${bold_green?}"
   else
     # For commands that return a non-zero exit status, set the exit status's
     # notifier to red:
-    local -r exit_status_color="${bold_red}"
+    local -r exit_status_color="${bold_red?}"
   fi
 
   echo -ne "${exit_status_color}"
   if [[ "${prompt_string}" -eq 1 ]]; then
     # $PS1:
-    echo -e " +${normal} "
+    echo -e " +${normal?} "
   elif [[ "${prompt_string}" -eq 2 ]]; then
     # $PS2:
-    echo -e " |${normal} "
+    echo -e " |${normal?} "
   else
     # Default:
-    echo -e " ?${normal} "
+    echo -e " ?${normal?} "
   fi
 }
 
 function _ps1() {
   local -r time='\\t'
 
-  echo -ne "${bold_white}${time} "
+  echo -ne "${bold_white?}${time} "
   echo -ne "$(_user-at-host-prompt)"
-  echo -e "${bold_white}:${normal}${PWD}"
+  echo -e "${bold_white?}:${normal?}${PWD}"
   echo -e "$(_exit-status-prompt 1 "${exit_status}")"
 }