diff --git a/README.md b/README.md
index 268507e..d15b889 100644
--- a/README.md
+++ b/README.md
@@ -58,6 +58,8 @@ which encodes most non-alphanumeric characters.
   to dot-path format and then serializes the values as above, e.g.,
   `{ foo: 'a', bar: { baz: 'b', fizz: [1, 2] } }` serializes to
   `foo=a&bar.baz=b&bar.fizz=1&bar.fizz=2`.
+- Empty objects are serialized to `undefined`, e.g.,
+  `{ foo: {}, bar: { baz: {} }, fizz: 1 }` serializes to `fizz=1`.
 - Serialization of keys containing a `.`
   is not supported and will throw an `UnserializableParamError`.
 - Serialization of nested arrays or objects nested inside arrays
@@ -67,6 +69,10 @@ which encodes most non-alphanumeric characters.
 - Serialization of `NaN`, `Infinity`, and `-Infinity`
   is not supported and will throw an `UnserializableParamError`.
 
+#### Why is the empty string and empty object parsed as undefined but not the empty array?
+
+TODO
+
 ### Compatible parsing strategy
 
 Serialization is guaranteed to be well-defined within each type, i.e.,
@@ -82,7 +88,7 @@ the consumer parsing the string, it can be unambigously parsed back to the origi
 ##### Primitive
 
 - `string | null`.
-  - Excludes zero-length strings.
+  - Excludes zero-length strings or treats them incidentally as `undefined`.
 - `number | null`.
 - `bigint | null`.
 - `boolean | null`.