diff --git a/src/commands/reports.rs b/src/commands/reports.rs
index 9aa0751..7feacce 100644
--- a/src/commands/reports.rs
+++ b/src/commands/reports.rs
@@ -191,7 +191,10 @@ pub async fn execute(cmd: ReportCommands, client: &CovalClient, ctx: &OutputCont
 fn validate_metadata_key(input: &serde_json::Map<String, serde_json::Value>) -> Result<()> {
     let is_metadata =
         input.get("compare_by").and_then(serde_json::Value::as_str) == Some("metadata");
-    let has_metadata_key = input.contains_key("metadata_key");
+    // An explicit null deserializes to None, so it is absent, not supplied.
+    let has_metadata_key = input
+        .get("metadata_key")
+        .is_some_and(|value| !value.is_null());
 
     if is_metadata && !has_metadata_key {
         anyhow::bail!("--metadata-key is required when --compare-by is metadata");
diff --git a/tests/cli_tests.rs b/tests/cli_tests.rs
index 6330661..0dcb0b5 100644
--- a/tests/cli_tests.rs
+++ b/tests/cli_tests.rs
@@ -3835,6 +3835,46 @@ fn test_reports_create_metadata_key_rejected_without_metadata_compare_by() {
         ));
 }
 
+#[test]
+fn test_reports_create_metadata_rejects_null_metadata_key() {
+    coval()
+        .arg("--api-key")
+        .arg("test_key")
+        .arg("reports")
+        .arg("create")
+        .arg("--name")
+        .arg("Bad Report")
+        .arg("--run-ids")
+        .arg("run1")
+        .arg("--compare-by")
+        .arg("metadata")
+        .arg("--input-json")
+        .arg(r#"{"metadata_key": null}"#)
+        .assert()
+        .failure()
+        .stderr(predicate::str::contains("--metadata-key is required"));
+}
+
+#[test]
+fn test_reports_create_allows_null_metadata_key_without_metadata_compare_by() {
+    coval()
+        .arg("--api-key")
+        .arg("test_key")
+        .arg("reports")
+        .arg("create")
+        .arg("--name")
+        .arg("Report")
+        .arg("--run-ids")
+        .arg("run1")
+        .arg("--compare-by")
+        .arg("run")
+        .arg("--input-json")
+        .arg(r#"{"metadata_key": null}"#)
+        .assert()
+        .failure()
+        .stderr(predicate::str::contains("--metadata-key can only be set").not());
+}
+
 #[tokio::test]
 async fn test_traces_search_sends_structured_filters_and_preserves_cursor() {
     let mock_server = MockServer::start().await;