diff --git a/Cargo.lock b/Cargo.lock
index 26666032..402ee9c9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5896,7 +5896,6 @@ dependencies = [
  "oslog",
  "paranoid-android",
  "parking_lot 0.11.2",
- "parking_lot 0.12.1",
  "rand 0.7.3",
  "range-set-blaze",
  "rust-fsm",
diff --git a/Earthfile b/Earthfile
index 1710abbd..c4571228 100644
--- a/Earthfile
+++ b/Earthfile
@@ -115,10 +115,12 @@ build-linux-arm64:
 # Unit tests
 unit-tests-linux-amd64:
     FROM +code-linux
+    ENV RUST_BACKTRACE=1
     RUN cargo test --target x86_64-unknown-linux-gnu --release -p veilid-server -p veilid-cli -p veilid-tools -p veilid-core
 
 # unit-tests-linux-arm64:
 #     FROM +code-linux
+#     ENV RUST_BACKTRACE=1
 #     RUN cargo test --target aarch64-unknown-linux-gnu --release -p veilid-server -p veilid-cli -p veilid-tools -p veilid-core
 
 # Package 
diff --git a/veilid-flutter/lib/veilid_ffi.dart b/veilid-flutter/lib/veilid_ffi.dart
index cfadb6a4..545641cc 100644
--- a/veilid-flutter/lib/veilid_ffi.dart
+++ b/veilid-flutter/lib/veilid_ffi.dart
@@ -338,8 +338,9 @@ Future<T> processFuturePlain<T>(Future<dynamic> future) {
     switch (list[0] as int) {
       case messageOk:
         {
-          if (list[1] == null) {
-            throw VeilidAPIExceptionInternal("Null MESSAGE_OK value");
+          if (list[1] == null && null is! T) {
+            throw const VeilidAPIExceptionInternal(
+                "Null MESSAGE_OK value on non-nullable type");
           }
           return list[1] as T;
         }
@@ -377,10 +378,15 @@ Future<T> processFutureJson<T>(
         }
       case messageOkJson:
         {
-          if (list[1] == null) {
-            throw VeilidAPIExceptionInternal("Null MESSAGE_OK_JSON value");
+          if (list[1] is! String) {
+            throw const VeilidAPIExceptionInternal(
+                "Non-string MESSAGE_OK_JSON value");
           }
           var ret = jsonDecode(list[1] as String);
+          if (ret == null) {
+            throw const VeilidAPIExceptionInternal(
+                "Null JSON object on non nullable type");
+          }
           return jsonConstructor(ret);
         }
       case messageErrJson:
@@ -416,7 +422,14 @@ Future<T?> processFutureOptJson<T>(
           if (list[1] == null) {
             return null;
           }
+          if (list[1] is! String) {
+            throw const VeilidAPIExceptionInternal(
+                "Non-string MESSAGE_OK_JSON optional value");
+          }
           var ret = jsonDecode(list[1] as String);
+          if (ret == null) {
+            return null;
+          }
           return jsonConstructor(ret);
         }
       case messageErrJson:
diff --git a/veilid-tools/src/assembly_buffer.rs b/veilid-tools/src/assembly_buffer.rs
index d2bdf077..44ed3d58 100644
--- a/veilid-tools/src/assembly_buffer.rs
+++ b/veilid-tools/src/assembly_buffer.rs
@@ -12,7 +12,7 @@ const MAX_LEN: usize = LengthType::MAX as usize;
 
 // XXX: keep statistics on all drops and why we dropped them
 // XXX: move to config eventually?
-const FRAGMENT_LEN: usize = 1280 - HEADER_LEN;
+pub const FRAGMENT_LEN: usize = 1280 - HEADER_LEN;
 const MAX_CONCURRENT_HOSTS: usize = 256;
 const MAX_ASSEMBLIES_PER_HOST: usize = 256;
 const MAX_BUFFER_PER_HOST: usize = 256 * 1024;
diff --git a/veilid-tools/src/tests/native/test_assembly_buffer.rs b/veilid-tools/src/tests/native/test_assembly_buffer.rs
index 73268516..95620ad8 100644
--- a/veilid-tools/src/tests/native/test_assembly_buffer.rs
+++ b/veilid-tools/src/tests/native/test_assembly_buffer.rs
@@ -86,7 +86,7 @@ pub async fn test_one_frag_out_in() {
     // Sending
     println!("sending");
     for _ in 0..10000 {
-        let random_len = (get_random_u32() % 1000) as usize + 1280;
+        let random_len = (get_random_u32() % 1000) as usize + FRAGMENT_LEN;
         let mut message = vec![1u8; random_len];
         random_bytes(&mut message);
         let remote_addr = random_sockaddr();
@@ -289,7 +289,7 @@ pub async fn test_many_frags_with_drops() {
     println!("sending");
     for _ in 0..1000 {
         let random_len = (get_random_u32() % 65536) as usize;
-        if random_len > 1280 {
+        if random_len > FRAGMENT_LEN {
             total_fragged += 1;
         }
         total_sent_size += random_len;