diff --git a/codegen/lib/graphql_swift_gen/templates/type.swift.erb b/codegen/lib/graphql_swift_gen/templates/type.swift.erb
index 4731dbb..50a1591 100644
--- a/codegen/lib/graphql_swift_gen/templates/type.swift.erb
+++ b/codegen/lib/graphql_swift_gen/templates/type.swift.erb
@@ -214,25 +214,29 @@ extension <%= schema_name %> {
   <% when 'INPUT_OBJECT' %>
     open class <%= type.name %> {
       <% type.required_input_fields.each do |field| %>
-       open var <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type) %>
+
+       open var <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type, non_null: true) %>
       <% end %>
       <% type.optional_input_fields.each do |field| %>
+
         open var <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type) %> {
           didSet {
-            <%= escape_reserved_word(field.camelize_name) %>Seen = true
+            serialize<%= escape_reserved_word(field.classify_name) %> = true
           }
         }
-        private var <%= escape_reserved_word(field.camelize_name) %>Seen: Bool = false
+        // Observes if the <%= escape_reserved_word(field.camelize_name) %> property was set, and indicates whether it should be serialized.
+        open var serialize<%= escape_reserved_word(field.classify_name) %>: Bool
       <% end %>
 
       public init(
         <% input_fields = type.required_input_fields + type.optional_input_fields # manually ordered with required fields first %>
         <% input_fields.each do |field| %>
-          <% seperator = field == input_fields.last ? "" : "," %>
+          <% separator = field == input_fields.last ? "" : "," %>
           <% if field.type.non_null? %>
-            <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type) %><%= seperator %>
+            <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type, non_null: true) %><%= separator %>
           <% else %>
-            <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type) %>? = nil<%= seperator %>
+            <%= escape_reserved_word(field.camelize_name) %>: <%= swift_input_type(field.type) %> = nil,
+            serialize<%= escape_reserved_word(field.classify_name) %>: Bool = false<%= separator %>
           <% end %>
         <% end %>
       ) {
@@ -240,10 +244,11 @@ extension <%= schema_name %> {
           self.<%= escape_reserved_word(field.camelize_name) %> = <%= escape_reserved_word(field.camelize_name) %>
         <% end %>
         <% type.optional_input_fields.each do |field| %>
+          self.serialize<%= escape_reserved_word(field.classify_name) %> = serialize<%= escape_reserved_word(field.classify_name) %>
           <% field_name = escape_reserved_word(field.camelize_name) %>
           if let <%= field_name %> = <%= field_name %> {
-            self.<%= field_name %>Seen = true
             self.<%= field_name %> = <%= field_name %>
+            self.serialize<%= escape_reserved_word(field.classify_name) %> = true
           }
         <% end %>
       }
@@ -254,7 +259,7 @@ extension <%= schema_name %> {
           fields.append("<%= field.name %>:<%= generate_build_input_code(field.camelize_name, field.type.unwrap_non_null) %>")
         <% end %>
         <% type.optional_input_fields.each do |field| %>
-          if <%= escape_reserved_word(field.camelize_name) %>Seen {
+          if serialize<%= escape_reserved_word(field.classify_name) %> {
             if let <%= escape_reserved_word(field.camelize_name) %> = <%= escape_reserved_word(field.camelize_name) %> {
               fields.append("<%= field.name %>:<%= generate_build_input_code(field.camelize_name, field.type.unwrap_non_null) %>")
             } else {
diff --git a/support/Tests/GraphQLSupportTests/IntegrationTests.swift b/support/Tests/GraphQLSupportTests/IntegrationTests.swift
index 02921eb..7c46bf3 100644
--- a/support/Tests/GraphQLSupportTests/IntegrationTests.swift
+++ b/support/Tests/GraphQLSupportTests/IntegrationTests.swift
@@ -68,9 +68,17 @@ class IntegrationTests: XCTestCase {
         XCTAssertEqual(queryString, "mutation{set_integer(input:{key:\"answer\",value:42,negate:true})}")
     }
 
-    func testInputObjectExplictNilConstructor() {
+    func testInputObjectOptionalFieldNilConstructor() {
         let query = Generated.buildMutation { $0
-            .setInteger(input: Generated.SetIntegerInput(key: "answer", value: 42, negate: .some(nil)))
+            .setInteger(input: Generated.SetIntegerInput(key: "answer", value: 42, negate: nil))
+        }
+        let queryString = String(describing: query)
+        XCTAssertEqual(queryString, "mutation{set_integer(input:{key:\"answer\",value:42})}")
+    }
+
+    func testInputObjectOptionalFieldExplictNilConstructor() {
+        let query = Generated.buildMutation { $0
+            .setInteger(input: Generated.SetIntegerInput(key: "answer", value: 42, negate: nil, serializeNegate: true))
         }
         let queryString = String(describing: query)
         XCTAssertEqual(queryString, "mutation{set_integer(input:{key:\"answer\",value:42,negate:null})}")