diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index e7f6d02c6..1759f3e35 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -4,7 +4,7 @@ on: [pull_request]
 jobs:
 
   analyze:
-    runs-on: macos-latest
+    runs-on: macos-11
     env:
       # Infer 1.0.1 cannot parse the iOS 15 SDK headers
       DEVELOPER_DIR: /Applications/Xcode_12.5.1.app
@@ -23,7 +23,7 @@ jobs:
       run: make oclint
 
   danger:
-    runs-on: macos-latest
+    runs-on: macos-11
     steps:
     - name: Checkout target branch
       uses: actions/checkout@v2
diff --git a/Bugsnag/Helpers/BSGRunContext.m b/Bugsnag/Helpers/BSGRunContext.m
index 50742b339..420eb15be 100644
--- a/Bugsnag/Helpers/BSGRunContext.m
+++ b/Bugsnag/Helpers/BSGRunContext.m
@@ -31,7 +31,6 @@
     atomic_store((_Atomic(typeof(field)) *)&field, newValue_); \
 } while (0)
 
-
 #pragma mark Forward declarations
 
 static uint64_t GetBootTime(void);
@@ -342,9 +341,11 @@ void BSGRunContextUpdateTimestamp() {
 }
 
 static void UpdateHostMemory() {
-    static mach_port_t host;
+    static _Atomic mach_port_t host_atomic = 0;
+    mach_port_t host = atomic_load(&host_atomic);
     if (!host) {
         host = mach_host_self();
+        atomic_store(&host_atomic, host);
     }
     
     vm_statistics_data_t host_vm;
@@ -357,7 +358,7 @@ static void UpdateHostMemory() {
     }
     
     size_t hostMemoryFree = host_vm.free_count * vm_kernel_page_size;
-    ATOMIC_SET(bsg_runContext->hostMemoryFree, hostMemoryFree);
+    bsg_runContext->hostMemoryFree = hostMemoryFree;
 }
 
 static void UpdateTaskMemory() {
diff --git a/Bugsnag/Helpers/BSGSerialization.h b/Bugsnag/Helpers/BSGSerialization.h
index 98dcf551d..9c37ba850 100644
--- a/Bugsnag/Helpers/BSGSerialization.h
+++ b/Bugsnag/Helpers/BSGSerialization.h
@@ -9,7 +9,9 @@ NS_ASSUME_NONNULL_BEGIN
  @param input a dictionary
  @return a new dictionary
  */
-NSMutableDictionary * BSGSanitizeDict(NSDictionary *input);
+NSMutableDictionary *BSGSanitizeDict(NSDictionary * input);
+
+NSMutableDictionary *_Nullable BSGSanitizePossibleDict(NSDictionary *_Nullable input);
 
 /**
  Cleans the object, including nested dictionary and array values
@@ -25,7 +27,8 @@ typedef struct _BSGTruncateContext {
     NSUInteger length;
 } BSGTruncateContext;
 
-NSString * BSGTruncateString(BSGTruncateContext *context, NSString *_Nullable string);
+NSString * BSGTruncateString(BSGTruncateContext *context, NSString * string);
+NSString *_Nullable BSGTruncatePossibleString(BSGTruncateContext *context, NSString *_Nullable string);
 
 id BSGTruncateStrings(BSGTruncateContext *context, id object);
 
diff --git a/Bugsnag/Helpers/BSGSerialization.m b/Bugsnag/Helpers/BSGSerialization.m
index c4d3265fe..997b279e8 100644
--- a/Bugsnag/Helpers/BSGSerialization.m
+++ b/Bugsnag/Helpers/BSGSerialization.m
@@ -20,10 +20,14 @@ id BSGSanitizeObject(id obj) {
     return nil;
 }
 
-NSMutableDictionary * BSGSanitizeDict(NSDictionary *input) {
+NSMutableDictionary * BSGSanitizePossibleDict(NSDictionary *input) {
     if (![input isKindOfClass:[NSDictionary class]]) {
         return nil;
     }
+    return BSGSanitizeDict(input);
+}
+
+NSMutableDictionary * BSGSanitizeDict(NSDictionary *input) {
     __block NSMutableDictionary *output =
         [NSMutableDictionary dictionaryWithCapacity:[input count]];
     [input enumerateKeysAndObjectsUsingBlock:^(id _Nonnull key, id _Nonnull obj,
@@ -47,10 +51,14 @@ id BSGSanitizeObject(id obj) {
     return output;
 }
 
-NSString * BSGTruncateString(BSGTruncateContext *context, NSString *string) {
+NSString * BSGTruncatePossibleString(BSGTruncateContext *context, NSString *string) {
     if (![string isKindOfClass:[NSString class]]) {
         return nil;
     }
+    return BSGTruncateString(context, string);
+}
+
+NSString * BSGTruncateString(BSGTruncateContext *context, NSString *string) {
     const NSUInteger inputLength = string.length;
     if (inputLength <= context->maxLength) return string;
     // Prevent chopping in the middle of a composed character sequence
diff --git a/Bugsnag/Payload/BugsnagEvent.m b/Bugsnag/Payload/BugsnagEvent.m
index d995c22df..df6c19ee1 100644
--- a/Bugsnag/Payload/BugsnagEvent.m
+++ b/Bugsnag/Payload/BugsnagEvent.m
@@ -729,12 +729,12 @@ - (void)truncateStrings:(NSUInteger)maxLength {
     };
     
     if (self.context) {
-        self.context = BSGTruncateString(&context, self.context);
+        self.context = BSGTruncatePossibleString(&context, self.context);
     }
     
     for (BugsnagError *error in self.errors) {
-        error.errorClass = BSGTruncateString(&context, error.errorClass);
-        error.errorMessage = BSGTruncateString(&context, error.errorMessage);
+        error.errorClass = BSGTruncatePossibleString(&context, error.errorClass);
+        error.errorMessage = BSGTruncatePossibleString(&context, error.errorMessage);
     }
     
     for (BugsnagBreadcrumb *breadcrumb in self.breadcrumbs) {
diff --git a/Tests/BugsnagTests/BugsnagCollectionsTests.m b/Tests/BugsnagTests/BugsnagCollectionsTests.m
index 7f5c802df..b376fb0cd 100644
--- a/Tests/BugsnagTests/BugsnagCollectionsTests.m
+++ b/Tests/BugsnagTests/BugsnagCollectionsTests.m
@@ -50,7 +50,10 @@ - (void)testDstEmpty {
 
 - (void)testDstNil {
     id src = @{@"a": @"one"};
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnonnull"
     XCTAssertEqualObjects(src, BSGDictMerge(src, nil), @"should copy");
+#pragma clang diagnostic pop
 }
 
 - (void)testSrcDict {
@@ -74,8 +77,11 @@ - (void)testSrcDstDict {
 // MARK: BSGJSONDictionary
 
 - (void)testBSGJSONDictionary {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wnonnull"
     XCTAssertNil(BSGJSONDictionary(nil));
-    
+#pragma clang diagnostic pop
+
     id validDictionary = @{
         @"name": @"foobar",
         @"count": @1,