fix(builder): Quote empty default values

Author: yash27-lab

clap_builder/src/util/escape.rs

@@ -8,7 +8,7 @@ impl<'s> Escape<'s> {
     }
 
     pub(crate) fn to_cow(self) -> Cow<'s, str> {
-        if self.0.contains(char::is_whitespace) {
+        if self.0.is_empty() || self.0.contains(char::is_whitespace) {
             Cow::Owned(format!("{:?}", self.0))
         } else {
             Cow::Borrowed(self.0)
@@ -18,7 +18,7 @@ impl<'s> Escape<'s> {
 
 impl std::fmt::Display for Escape<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        if self.0.contains(char::is_whitespace) {
+        if self.0.is_empty() || self.0.contains(char::is_whitespace) {
             std::fmt::Debug::fmt(self.0, f)
         } else {
             self.0.fmt(f)

tests/builder/help.rs

@@ -2044,7 +2044,7 @@ fn empty_default_value() {
 Usage: default [OPTIONS]
 
 Options:
-      --arg <argument>  Pass an argument to the program. [default: ]
+      --arg <argument>  Pass an argument to the program. [default: ""]
   -h, --help            Print help
   -V, --version         Print version