diff --git a/src/format/json.rs b/src/format/json.rs
index 1976ddf..7e9ebbc 100644
--- a/src/format/json.rs
+++ b/src/format/json.rs
@@ -174,6 +174,11 @@ impl<'b, 'v> VisitValue<'v> for KeyValueVisitor<'b> {
         Ok(())
     }
 
+    fn visit_null(&mut self) -> Result<(), kv::Error> {
+        self.0.extend_from_slice(b"null");
+        Ok(())
+    }
+
     fn visit_u64(&mut self, value: u64) -> Result<(), kv::Error> {
         let mut itoa = itoa::Buffer::new();
         self.0.extend_from_slice(itoa.format(value).as_bytes());
diff --git a/src/format/logfmt.rs b/src/format/logfmt.rs
index b3fb716..c668dc6 100644
--- a/src/format/logfmt.rs
+++ b/src/format/logfmt.rs
@@ -161,6 +161,11 @@ impl<'b, 'v> VisitValue<'v> for KeyValueVisitor<'b> {
         Ok(())
     }
 
+    fn visit_null(&mut self) -> Result<(), kv::Error> {
+        self.0.extend_from_slice(b"null");
+        Ok(())
+    }
+
     fn visit_u64(&mut self, value: u64) -> Result<(), kv::Error> {
         let mut itoa = itoa::Buffer::new();
         self.0.extend_from_slice(itoa.format(value).as_bytes());
diff --git a/src/tests.rs b/src/tests.rs
index 2ef4967..68d6a79 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -199,7 +199,7 @@ fn format_logfmt() {
     format_test::<LogFmt, _>(&[
         "lvl=\"INFO\" msg=\"some\\r\\n\\t\\nmessage\" target=\"some_target1\" module=\"module_path1\" key1=\"value1\" file=\"file1:123\"\n",
         "lvl=\"INFO\" msg=\"some\\r\\n\\t\\nmessage\" target=\"some_target1\" module=\"module_path1\" key1=\"value1\"\n",
-        "lvl=\"WARN\" msg=\"arguments2 with \\\"quotes\\\"\" target=\"second_target\" module=\"module_path1\" key2a=\"value2\" key2b=123 key3c=-123 key3d=123.0 key2e=true key2f=false key2g=\"c\" key2\\\"g=\"MyDisplay\" file=\"file2:111\"\n",
+        "lvl=\"WARN\" msg=\"arguments2 with \\\"quotes\\\"\" target=\"second_target\" module=\"module_path1\" key2a=\"value2\" key2b=123 key3c=-123 key3d=123.0 key2e=true key2f=false key2g=\"c\" key2\\\"g=\"MyDisplay\" null_key=null file=\"file2:111\"\n",
         "lvl=\"ERROR\" msg=\"panicking!\" target=\"panic\" module=\"\" file=\"??:0\"\n",
     ], add_timestamp);
 }
@@ -209,7 +209,7 @@ fn format_json() {
     format_test::<Json, _>(&[
         "{\"level\":\"INFO\",\"message\":\"some\\r\\n\\t\\nmessage\",\"target\":\"some_target1\",\"module\":\"module_path1\",\"key1\":\"value1\",\"file\":\"file1\",\"line\":\"123\"}\n",
         "{\"level\":\"INFO\",\"message\":\"some\\r\\n\\t\\nmessage\",\"target\":\"some_target1\",\"module\":\"module_path1\",\"key1\":\"value1\"}\n",
-        "{\"level\":\"WARN\",\"message\":\"arguments2 with \\\"quotes\\\"\",\"target\":\"second_target\",\"module\":\"module_path1\",\"key2a\":\"value2\",\"key2b\":123,\"key3c\":-123,\"key3d\":123.0,\"key2e\":true,\"key2f\":false,\"key2g\":\"c\",\"key2\\\"g\":\"MyDisplay\",\"file\":\"file2\",\"line\":\"111\"}\n",
+        "{\"level\":\"WARN\",\"message\":\"arguments2 with \\\"quotes\\\"\",\"target\":\"second_target\",\"module\":\"module_path1\",\"key2a\":\"value2\",\"key2b\":123,\"key3c\":-123,\"key3d\":123.0,\"key2e\":true,\"key2f\":false,\"key2g\":\"c\",\"key2\\\"g\":\"MyDisplay\",\"null_key\":null,\"file\":\"file2\",\"line\":\"111\"}\n",
         "{\"level\":\"ERROR\",\"message\":\"panicking!\",\"target\":\"panic\",\"module\":\"\",\"file\":\"??\",\"line\":\"0\"}\n",
     ], add_timestamp_json);
 }
@@ -219,7 +219,7 @@ fn format_gcloud() {
     format_test::<Gcloud, _>(&[
         "{\"severity\":\"INFO\",\"message\":\"some\\r\\n\\t\\nmessage\",\"target\":\"some_target1\",\"module\":\"module_path1\",\"key1\":\"value1\",\"sourceLocation\":{\"file\":\"file1\",\"line\":\"123\"}}\n",
         "{\"severity\":\"INFO\",\"message\":\"some\\r\\n\\t\\nmessage\",\"target\":\"some_target1\",\"module\":\"module_path1\",\"key1\":\"value1\"}\n",
-        "{\"severity\":\"WARNING\",\"message\":\"arguments2 with \\\"quotes\\\"\",\"target\":\"second_target\",\"module\":\"module_path1\",\"key2a\":\"value2\",\"key2b\":123,\"key3c\":-123,\"key3d\":123.0,\"key2e\":true,\"key2f\":false,\"key2g\":\"c\",\"key2\\\"g\":\"MyDisplay\",\"sourceLocation\":{\"file\":\"file2\",\"line\":\"111\"}}\n",
+        "{\"severity\":\"WARNING\",\"message\":\"arguments2 with \\\"quotes\\\"\",\"target\":\"second_target\",\"module\":\"module_path1\",\"key2a\":\"value2\",\"key2b\":123,\"key3c\":-123,\"key3d\":123.0,\"key2e\":true,\"key2f\":false,\"key2g\":\"c\",\"key2\\\"g\":\"MyDisplay\",\"null_key\":null,\"sourceLocation\":{\"file\":\"file2\",\"line\":\"111\"}}\n",
         "{\"severity\":\"CRITICAL\",\"message\":\"panicking!\",\"target\":\"panic\",\"module\":\"\",\"sourceLocation\":{\"file\":\"??\",\"line\":\"0\"}}\n",
     ], add_timestamp_json);
 }
@@ -258,6 +258,7 @@ where
             "key2\"g",
             &(&log::kv::Value::from_display(&MyDisplay) as &dyn kv::ToValue),
         ),
+        ("null_key", &None::<&str>),
     ];
     let kvs: &dyn kv::Source = &kvs;
     let record2 = Record::builder()