diff --git a/CHANGELOG.md b/CHANGELOG.md
index a68ecfc..bc5b5e0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,12 @@
 
 Each release has a `## [version]` section. When a `v*.*.*` tag is pushed, the Publish workflow copies that section into the GitHub release, and it fails if the section is missing.
 
+## [Unreleased]
+
+### Docs
+
+- Caveats document 15-argument `TypeLoadException`, C# optional parameters, and `tryGet` / `exists` on a null target (#110).
+
 ## [6.0.0]
 
 ### Breaking
diff --git a/README.md b/README.md
index d110674..9be5953 100644
--- a/README.md
+++ b/README.md
@@ -126,6 +126,9 @@ You can still `open Dynamitey` for `Build`, `Dynamic.Curry`, `DynamicObjects.Dic
 
 - The DLR cannot see **explicit interface members** (same as C# `dynamic`).
 - **Not trim-safe or NativeAOT-safe.**
+- **15 or more arguments** throw `TypeLoadException` (ImpromptuInterface was never shipped). Fourteen work.
+- **C# optional parameters** must all be passed. The DLR does not fill defaults.
+- `tryGet` / `exists` on a **null target** throw `NullReferenceException` (not `None` / `false`).
 - Do not build member names from untrusted input. [SECURITY.md](SECURITY.md).
 - Historical: .NET Core 2.0.0–2.0.2 broke `dynamic` on nested types inside generics ([#11](https://github.com/fsprojects/FSharp.Interop.Dynamic/issues/11)). Current TFMs are fine.
 
diff --git a/docfx/docs/caveats.md b/docfx/docs/caveats.md
index ce20960..f0d28cc 100644
--- a/docfx/docs/caveats.md
+++ b/docfx/docs/caveats.md
@@ -18,6 +18,18 @@ Annotate `'T` / `unit` so the binder and the conversion agree.
 
 `Dyn.exists "x"` is true if `InvokeGet` succeeded, including when the value is null. `tryGet` returns `Some null` for a reference type. That is different from missing.
 
+## Null target
+
+`Dyn.tryGet` and `Dyn.exists` on a **null target** throw `NullReferenceException`. That is not a binder miss, so it is not `None` / `false`. Same for `Dyn.set`. A present null *value* is still `Some null` / `exists` true. Changing the null-target contract is [#111](https://github.com/fsprojects/FSharp.Interop.Dynamic/issues/111).
+
+## More than 14 arguments
+
+A call with **15 or more** arguments throws `TypeLoadException: Cannot Emit long delegates without ImpromptuInterface installed`. Fourteen arguments work. Dynamitey 3.0.3 never shipped ImpromptuInterface with this package. A fix belongs in a newer Dynamitey, not in a vendor here ([#29](https://github.com/fsprojects/FSharp.Interop.Dynamic/issues/29)).
+
+## C# optional parameters
+
+The DLR does not fill CLR optional defaults. `obj?Opt(5)` and `namedArg "a" 5` both fail (`No overload takes 1 arguments`) when `Opt` is `Opt(int a, int b = 0)`. Pass every argument. Named args work when the full set is present.
+
 ## Function-typed results delay the call
 
 If F# infers `'TResult` as a function, `?` / `Dyn.get` / `Dyn.invokeMember` return a callable. A missing member in that mode used to look like `Some (fun …)` until you applied it. `tryGet` does `InvokeGet` first, so a missing member is `None` even when `'T` is a function.
diff --git a/docfx/docs/getting-started.md b/docfx/docs/getting-started.md
index d29e278..12b4033 100644
--- a/docfx/docs/getting-started.md
+++ b/docfx/docs/getting-started.md
@@ -69,4 +69,4 @@ let _: unit = items?Add("x")
 - [Operators](operators.md) — `?`, `?<-`, `!?` in detail
 - [Dyn](dyn.md) — the functions behind those operators
 - [tryGet and exists](tryget.md) — the issue #27 surface
-- [Caveats](caveats.md) — explicit interface members, AOT, conversion vs missing
+- [Caveats](caveats.md) — explicit interface members, AOT, conversion vs missing, 15-arg, optionals, null target
diff --git a/docfx/docs/tryget.md b/docfx/docs/tryget.md
index 448fe02..9543fa6 100644
--- a/docfx/docs/tryget.md
+++ b/docfx/docs/tryget.md
@@ -27,6 +27,7 @@ Lookup is `Dynamic.InvokeGet` only. Then the existing conversion / callable wrap
 | Member present, value cannot convert to `'T` | throws (`InvalidCastException` or a binder exception) — **not** `None` |
 | Member missing, `'T` is a function type | `None` immediately (does not return a lazy callable) |
 | Getter throws something else | that exception propagates |
+| Target is null | `NullReferenceException` (not `None`). [#110](https://github.com/fsprojects/FSharp.Interop.Dynamic/issues/110), [#111](https://github.com/fsprojects/FSharp.Interop.Dynamic/issues/111) |
 
 ## `Dyn.exists`
 
@@ -35,7 +36,7 @@ o |> Dyn.exists "myProp"   // true
 o |> Dyn.exists "nope"     // false
 ```
 
-True when `InvokeGet` succeeds. A present null is still present. A throwing getter is not reported as missing.
+True when `InvokeGet` succeeds. A present null is still present. A throwing getter is not reported as missing. A **null target** throws `NullReferenceException`, not `false`.
 
 `exists` does not convert the value. That is the difference from `tryGet >> Option.isSome` when conversion would fail: `exists` can be true while `tryGet` as `int` throws.