diff --git a/lib/api.dart b/lib/api.dart
index 01b551a9..b7ef059d 100644
--- a/lib/api.dart
+++ b/lib/api.dart
@@ -423,14 +423,12 @@ class InvenTreeAPI {
 
 
   // Perform a PATCH request
-  Future<dynamic> patch(String url, {Map<String, String>? body, int expectedStatusCode=200}) async {
+  Future<dynamic> patch(String url, {Map<String, String> body = const {}, int expectedStatusCode=200}) async {
     var _url = makeApiUrl(url);
     var _body = Map<String, String>();
 
     // Copy across provided data
-    if (body != null) {
-      body.forEach((K, V) => _body[K] = V);
-    }
+    body.forEach((K, V) => _body[K] = V);
 
     print("PATCH: " + _url);
 
@@ -512,18 +510,18 @@ class InvenTreeAPI {
       return null;
     });
 
-    if (response == null) {
-      print("null response from PATCH ${_url}");
-      return null;
-    }
+    var responseData = await responseToJson(response);
 
     if (response.statusCode != expectedStatusCode) {
       showStatusCodeError(response.statusCode);
+
+      print("PATCH to ${_url} returned status code ${response.statusCode}");
+      print("Data:");
+      print(responseData);
+
       return null;
     }
 
-    var responseData = await responseToJson(response);
-
     return responseData;
   }
 
@@ -558,7 +556,7 @@ class InvenTreeAPI {
    * Perform a HTTP POST request
    * Returns a json object (or null if unsuccessful)
    */
-  Future<dynamic> post(String url, {Map<String, dynamic>? body, int expectedStatusCode=201}) async {
+  Future<dynamic> post(String url, {Map<String, dynamic> body = const {}, int expectedStatusCode=201}) async {
 
     var _url = makeApiUrl(url);
 
@@ -600,10 +598,6 @@ class InvenTreeAPI {
       return null;
     });
 
-    if (request == null) {
-      return null;
-    }
-
     var data = json.encode(body);
 
     // Set headers
@@ -647,13 +641,18 @@ class InvenTreeAPI {
       return null;
     }
 
+    var responseData = await responseToJson(response);
+
     if (response.statusCode != expectedStatusCode) {
       showStatusCodeError(response.statusCode);
+
+      print("POST to ${_url} returned status code ${response.statusCode}");
+      print("Data:");
+      print(responseData);
+
       return null;
     }
 
-    var responseData = await responseToJson(response);
-
     return responseData;
   }
 
@@ -690,13 +689,13 @@ class InvenTreeAPI {
    * and return the Response object
    * (or null if the request fails)
    */
-  Future<HttpClientResponse?> getResponse(String url, {Map<String, String>? params}) async {
+  Future<HttpClientResponse?> getResponse(String url, {Map<String, String> params = const {}}) async {
     var _url = makeApiUrl(url);
 
     print("GET: ${_url}");
 
     // If query parameters are supplied, form a query string
-    if (params != null && params.isNotEmpty) {
+    if (params.isNotEmpty) {
       String query = '?';
 
       params.forEach((K, V) => query += K + '=' + V + '&');
@@ -785,10 +784,6 @@ class InvenTreeAPI {
 
   dynamic responseToJson(HttpClientResponse response) async {
 
-    if (response == null) {
-      return null;
-    }
-
     String body = await response.transform(utf8.decoder).join();
 
     try {
@@ -813,7 +808,7 @@ class InvenTreeAPI {
    * Perform a HTTP GET request
    * Returns a json object (or null if did not complete)
    */
-  Future<dynamic> get(String url, {Map<String, String>? params, int expectedStatusCode=200}) async {
+  Future<dynamic> get(String url, {Map<String, String> params = const {}, int expectedStatusCode=200}) async {
 
     var response = await getResponse(url, params: params);
 
diff --git a/lib/inventree/model.dart b/lib/inventree/model.dart
index 2fc5a81f..678739a6 100644
--- a/lib/inventree/model.dart
+++ b/lib/inventree/model.dart
@@ -142,11 +142,7 @@ class InvenTreeModel {
 
 
   // Search this Model type in the database
-  Future<List<InvenTreeModel>> search(BuildContext context, String searchTerm, {Map<String, String>? filters}) async {
-
-    if (filters == null) {
-      filters = {};
-    }
+  Future<List<InvenTreeModel>> search(BuildContext context, String searchTerm, {Map<String, String> filters = const {}}) async {
 
     filters["search"] = searchTerm;
 
@@ -178,7 +174,7 @@ class InvenTreeModel {
   }
 
   // POST data to update the model
-  Future<bool> update({Map<String, String>? values}) async {
+  Future<bool> update({Map<String, String> values = const {}}) async {
 
     var addr = path.join(URL, pk.toString());
 
@@ -198,7 +194,7 @@ class InvenTreeModel {
   }
 
   // Return the detail view for the associated pk
-  Future<InvenTreeModel?> get(int pk, {Map<String, String>? filters}) async {
+  Future<InvenTreeModel?> get(int pk, {Map<String, String> filters = const {}}) async {
 
     // TODO - Add "timeout"
     // TODO - Add error catching
@@ -211,11 +207,9 @@ class InvenTreeModel {
 
     var params = defaultGetFilters();
 
-    if (filters != null) {
-      // Override any default values
-      for (String key in filters.keys) {
-        params[key] = filters[key] ?? '';
-      }
+    // Override any default values
+    for (String key in filters.keys) {
+      params[key] = filters[key] ?? '';
     }
 
     print("GET: $url ${params.toString()}");
@@ -250,13 +244,11 @@ class InvenTreeModel {
     return createFromJson(response);
   }
 
-  Future<InvenTreePageResponse?> listPaginated(int limit, int offset, {Map<String, String>? filters = null}) async {
+  Future<InvenTreePageResponse?> listPaginated(int limit, int offset, {Map<String, String> filters = const {}}) async {
     var params = defaultListFilters();
 
-    if (filters != null) {
-      for (String key in filters.keys) {
-        params[key] = filters[key] ?? '';
-      }
+    for (String key in filters.keys) {
+      params[key] = filters[key] ?? '';
     }
 
     params["limit"] = "${limit}";
@@ -288,18 +280,12 @@ class InvenTreeModel {
   }
 
   // Return list of objects from the database, with optional filters
-  Future<List<InvenTreeModel>> list({Map<String, String>? filters}) async {
-
-    if (filters == null) {
-      filters = {};
-    }
+  Future<List<InvenTreeModel>> list({Map<String, String> filters = const {}}) async {
 
     var params = defaultListFilters();
 
-    if (filters != null) {
-      for (String key in filters.keys) {
-        params[key] = filters[key] ?? '';
-      }
+    for (String key in filters.keys) {
+      params[key] = filters[key] ?? '';
     }
 
     print("LIST: $URL ${params.toString()}");
diff --git a/lib/widget/search.dart b/lib/widget/search.dart
index f97ea59b..97ccde01 100644
--- a/lib/widget/search.dart
+++ b/lib/widget/search.dart
@@ -27,9 +27,20 @@ class PartSearchDelegate extends SearchDelegate<InvenTreePart?> {
   bool _searching = false;
 
   // Custom filters for the part search
-  Map<String, String> filters = {};
+  Map<String, String> _filters = {};
 
-  PartSearchDelegate(this.context, {this.filters = const {}});
+  PartSearchDelegate(this.context, {Map<String, String> filters = const {}}) {
+
+    // Copy filter values
+    for (String key in filters.keys) {
+
+      String? value = filters[key];
+
+      if (value != null) {
+        _filters[key] = value;
+      }
+    }
+  }
 
   @override
   String get searchFieldLabel => L10().searchParts;
@@ -58,10 +69,9 @@ class PartSearchDelegate extends SearchDelegate<InvenTreePart?> {
 
     showResults(context);
 
-    // Enable cascading part search by default
-    filters["cascade"] = "true";
+    _filters["cascade"] = "true";
 
-    final results = await InvenTreePart().search(context, query, filters: filters);
+    final results = await InvenTreePart().search(context, query, filters: _filters);
 
     partResults.clear();
 
@@ -208,11 +218,18 @@ class StockSearchDelegate extends SearchDelegate<InvenTreeStockItem?> {
   bool _searching = false;
 
   // Custom filters for the stock item search
-  Map<String, String>? filters;
+  Map<String, String> _filters = {};
 
-  StockSearchDelegate(this.context, {this.filters}) {
-    if (filters == null) {
-      filters = {};
+  StockSearchDelegate(this.context, {Map<String, String> filters = const {}}) {
+
+    // Copy filter values
+    for (String key in filters.keys) {
+
+      String? value = filters[key];
+
+      if (value != null) {
+        _filters[key] = value;
+      }
     }
   }
 
@@ -243,12 +260,10 @@ class StockSearchDelegate extends SearchDelegate<InvenTreeStockItem?> {
     showResults(context);
 
     // Enable cascading part search by default
-    if (filters != null) {
-      filters?["cascade"] = "true";
-    }
+    _filters["cascade"] = "true";
 
     final results = await InvenTreeStockItem().search(
-        context, query, filters: filters);
+        context, query, filters: _filters);
 
     itemResults.clear();