Fix nothing string comparison (#3750)

crates/nu-data/src/base.rs

@@ -164,6 +164,10 @@ pub fn coerce_compare_primitive(
         (Boolean(left), Boolean(right)) => CompareValues::Booleans(*left, *right),
         (Boolean(left), Nothing) => CompareValues::Booleans(*left, false),
         (Nothing, Boolean(right)) => CompareValues::Booleans(false, *right),
+        (String(left), Nothing) => CompareValues::String(left.clone(), std::string::String::new()),
+        (Nothing, String(right)) => {
+            CompareValues::String(std::string::String::new(), right.clone())
+        }
         (FilePath(left), String(right)) => {
             CompareValues::String(left.as_path().display().to_string(), right.clone())
         }

tests/shell/pipeline/commands/internal.rs

@@ -1083,6 +1083,30 @@ fn manysubcommand() {
     assert_eq!(actual.out, "localhost loaded");
 }
 
+#[test]
+fn nothing_string_1() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        $nothing == "foo"
+        "#)
+    );
+
+    assert_eq!(actual.out, "false");
+}
+
+#[test]
+fn nothing_string_2() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        "" == $nothing
+        "#)
+    );
+
+    assert_eq!(actual.out, "true");
+}
+
 mod parse {
     use nu_test_support::nu;