ffi: remove dead null check in callback arguments

InvokeCallback tested `args[i] == nullptr` and mapped the argument to
JS `null`. `args` is libffi's avalue array, and libffi always points
each slot at its own storage for the corresponding argument, so the
slot pointers are never null and the branch never ran.

The check also read as a guarantee the code does not provide: a NULL
pointer argument surfaces as the BigInt `0n`, because ToJSArgument
converts `ffi_type_pointer` values with BigInt::NewFromUnsigned. Drop
the branch rather than reimplementing it in ToJSArgument, which would
change behavior by making pointer parameters arrive as either a BigInt
or `null`.

Signed-off-by: Trivikram Kamat <16024985+trivikr@users.noreply.github.com>
Assisted-by: claude:opus-5

Author: trivikr

src/node_ffi.cc

@@ -32,7 +32,6 @@ using v8::Local;
 using v8::LocalVector;
 using v8::Maybe;
 using v8::MaybeLocal;
-using v8::Null;
 using v8::Object;
 using v8::PropertyAttribute;
 using v8::ReadOnly;
@@ -665,13 +664,11 @@ void DynamicLibrary::InvokeCallback(ffi_cif* cif,
   size_t expected_args = cb->args.size();
   LocalVector<Value> callback_args(isolate, expected_args);
 
+  // libffi always points `args[i]` at its own storage for the value of
+  // argument `i`, so the slot pointers themselves are never null. A NULL
+  // pointer argument surfaces as the BigInt `0n` via ToJSArgument.
   for (size_t i = 0; i < expected_args; i++) {
-    if (args[i] == nullptr) {
-      callback_args[i] = Null(isolate);
-      continue;
-    } else {
-      callback_args[i] = ToJSArgument(isolate, cb->args[i], args[i]);
-    }
+    callback_args[i] = ToJSArgument(isolate, cb->args[i], args[i]);
   }
 
   TryCatch try_catch(isolate);