fix(repl): fix null eval result (#13804)

Co-authored-by: Satya Rohith <me@satyarohith.com>

cli/cdp.rs

@@ -4,6 +4,7 @@
 use deno_core::serde_json;
 use deno_core::serde_json::Value;
 use serde::Deserialize;
+use serde::Deserializer;
 use serde::Serialize;
 
 /// https://chromedevtools.github.io/devtools-protocol/tot/Runtime/#method-awaitPromise
@@ -245,6 +246,7 @@ pub struct RemoteObject {
   pub kind: String,
   pub subtype: Option<String>,
   pub class_name: Option<String>,
+  #[serde(default, deserialize_with = "deserialize_some")]
   pub value: Option<Value>,
   pub unserializable_value: Option<UnserializableValue>,
   pub description: Option<String>,
@@ -253,6 +255,16 @@ pub struct RemoteObject {
   pub custom_preview: Option<CustomPreview>,
 }
 
+// Any value that is present is considered Some value, including null.
+// ref: https://github.com/serde-rs/serde/issues/984#issuecomment-314143738
+fn deserialize_some<'de, T, D>(deserializer: D) -> Result<Option<T>, D::Error>
+where
+  T: Deserialize<'de>,
+  D: Deserializer<'de>,
+{
+  Deserialize::deserialize(deserializer).map(Some)
+}
+
 /// https://chromedevtools.github.io/devtools-protocol/tot/Runtime/#type-ObjectPreview
 #[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]

cli/tests/integration/repl_tests.rs

@@ -33,6 +33,17 @@ fn pty_multiline() {
   });
 }
 
+#[test]
+fn pty_null() {
+  util::with_pty(&["repl"], |mut console| {
+    console.write_line("null");
+    console.write_line("close();");
+
+    let output = console.read_all_output();
+    assert!(output.contains("null"));
+  });
+}
+
 #[test]
 fn pty_unpaired_braces() {
   util::with_pty(&["repl"], |mut console| {