diff --git a/Rakefile b/Rakefile
index bdb054b..a9b8b28 100644
--- a/Rakefile
+++ b/Rakefile
@@ -25,6 +25,12 @@ task :generate do
         deserialize_expr: ->(expr) { "LocalDateTime.parse(jsonAsString(#{expr}, key))" },
         imports: ['java.time.LocalDateTime'],
       )
+    ],
+    custom_annotations: [
+      GraphQLJavaGen::Annotation.new(
+        'Nullable',
+        imports: ['com.shopify.graphql.support.Nullable']
+      ) { |field| !field.type.non_null? },
     ]
   ).save('support/src/test/java/com/shopify/graphql/support/Generated.java')
 
diff --git a/codegen/lib/graphql_java_gen.rb b/codegen/lib/graphql_java_gen.rb
index 59c9e23..b814aff 100644
--- a/codegen/lib/graphql_java_gen.rb
+++ b/codegen/lib/graphql_java_gen.rb
@@ -253,10 +253,17 @@ def java_implements(type)
     "implements #{interfaces.to_a.join(', ')} "
   end
 
-  def java_annotations(field)
-    @annotations.map do |annotation|
+  def java_annotations(field, in_argument: false)
+    annotations = @annotations.map do |annotation|
       "@#{annotation.name}" if annotation.annotate?(field)
-    end.compact.join("\n")
+    end.compact
+    return "" unless annotations.any?
+
+    if in_argument
+      annotations.join(" ") + " "
+    else
+      annotations.join("\n")
+    end
   end
 
   def type_names_set
diff --git a/codegen/lib/graphql_java_gen/templates/APISchema.java.erb b/codegen/lib/graphql_java_gen/templates/APISchema.java.erb
index 945bfac..5357f70 100644
--- a/codegen/lib/graphql_java_gen/templates/APISchema.java.erb
+++ b/codegen/lib/graphql_java_gen/templates/APISchema.java.erb
@@ -237,7 +237,7 @@ public class <%= schema_name %> {
 
                 <% fields.each do |field| %>
                     <%= java_doc(field) %>
-                    <%= java_annotations(field) -%>
+                    <%= java_annotations(field) %>
                     public <%= java_output_type(field.type) %> get<%= field.classify_name %>() {
                       return (<%= java_output_type(field.type) %>) get("<%= field.name %>");
                     }
@@ -265,6 +265,7 @@ public class <%= schema_name %> {
                 <% end %>
                 <% type.optional_input_fields.each do |field| %>
                   private <%= java_input_type(field.type) %> <%= escape_reserved_word(field.camelize_name) %>;
+                  private boolean <%= field.camelize_name %>Seen = false;
                 <% end %>
 
                 <% unless type.required_input_fields.empty? %>
@@ -276,22 +277,25 @@ public class <%= schema_name %> {
                 <% end %>
 
                 <% type.required_input_fields.each do |field| %>
+                  <%= java_annotations(field) %>
                   public <%= java_input_type(field.type) %> get<%= field.classify_name %>() {
                       return <%= escape_reserved_word(field.camelize_name) %>;
                   }
 
-                  public <%= type.name %> set<%= field.classify_name %>(<%= java_input_type(field.type) %> <%= escape_reserved_word(field.camelize_name) %>) {
+                  public <%= type.name %> set<%= field.classify_name %>(<%= java_annotations(field, in_argument: true) %><%= java_input_type(field.type) %> <%= escape_reserved_word(field.camelize_name) %>) {
                       this.<%= escape_reserved_word(field.camelize_name) %> = <%= escape_reserved_word(field.camelize_name) %>;
                       return this;
                   }
                 <% end %>
                 <% type.optional_input_fields.each do |field| %>
+                  <%= java_annotations(field) %>
                   public <%= java_input_type(field.type) %> get<%= field.classify_name %>() {
                       return <%= escape_reserved_word(field.camelize_name) %>;
                   }
 
-                  public <%= type.name %> set<%= field.classify_name %>(<%= java_input_type(field.type) %> <%= escape_reserved_word(field.camelize_name) %>) {
+                  public <%= type.name %> set<%= field.classify_name %>(<%= java_annotations(field, in_argument: true) %><%= java_input_type(field.type) %> <%= escape_reserved_word(field.camelize_name) %>) {
                       this.<%= escape_reserved_word(field.camelize_name) %> = <%= escape_reserved_word(field.camelize_name) %>;
+                      this.<%= field.camelize_name %>Seen = true;
                       return this;
                   }
                 <% end %>
@@ -306,11 +310,15 @@ public class <%= schema_name %> {
                     <%= generate_build_input_code(escape_reserved_word(field.camelize_name), field.type) %>
                   <% end %>
                   <% type.optional_input_fields.each do |field| %>
-                    if (<%= escape_reserved_word(field.camelize_name) %> != null) {
+                    if (this.<%= field.camelize_name %>Seen) {
                       _queryBuilder.append(separator);
                       separator = ",";
                       _queryBuilder.append("<%= field.name %>:");
-                      <%= generate_build_input_code(escape_reserved_word(field.camelize_name), field.type) %>
+                      if (<%= escape_reserved_word(field.camelize_name) %> != null) {
+                        <%= generate_build_input_code(escape_reserved_word(field.camelize_name), field.type) %>
+                      } else {
+                        _queryBuilder.append("null");
+                      }
                     }
                   <% end %>
                   _queryBuilder.append('}');
diff --git a/codegen/test/support/schema.rb b/codegen/test/support/schema.rb
index 21d3e2c..2efd2c6 100644
--- a/codegen/test/support/schema.rb
+++ b/codegen/test/support/schema.rb
@@ -91,6 +91,7 @@ module Schema
       argument :value, !types.Int
       argument :ttl, TimeType
       argument :negate, types.Boolean, default_value: false
+      argument :api_client, types.String
     end
 
     MutationType = GraphQL::ObjectType.define do
diff --git a/support/src/main/java/com/shopify/graphql/support/Nullable.java b/support/src/main/java/com/shopify/graphql/support/Nullable.java
new file mode 100644
index 0000000..f1b7b04
--- /dev/null
+++ b/support/src/main/java/com/shopify/graphql/support/Nullable.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.shopify.graphql.support;
+
+import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PACKAGE;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Denotes that a parameter, field or method return value can be null.
+ * <p>
+ * When decorating a method call parameter, this denotes that the parameter can
+ * legitimately be null and the method will gracefully deal with it. Typically
+ * used on optional parameters.
+ * <p>
+ * When decorating a method, this denotes the method might legitimately return
+ * null.
+ * <p>
+ * This is a marker annotation and it has no specific attributes.
+ */
+@Documented
+@Retention(RUNTIME)
+@Target({METHOD, PARAMETER, FIELD, ANNOTATION_TYPE, PACKAGE})
+public @interface Nullable {
+}
+
diff --git a/support/src/test/java/com/shopify/graphql/support/AnnotationTest.java b/support/src/test/java/com/shopify/graphql/support/AnnotationTest.java
new file mode 100644
index 0000000..1b77f6f
--- /dev/null
+++ b/support/src/test/java/com/shopify/graphql/support/AnnotationTest.java
@@ -0,0 +1,28 @@
+package com.shopify.graphql.support;
+
+import org.junit.Test;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Method;
+
+import static junit.framework.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import com.shopify.graphql.support.Generated;
+
+public class AnnotationTest {
+    @Test
+    public void testAppliesAnnotation() throws Exception {
+      Class<Generated> obj = Generated.class;
+      boolean foundNullable = false;
+      for (Class klass: obj.getDeclaredClasses()) {
+        for (Method method : klass.getDeclaredMethods()) {
+          if (method.isAnnotationPresent(Nullable.class)) {
+            foundNullable = true;
+            break;
+          }
+        }
+      }
+      assertTrue("Should have found a class with @Nullable annotation in Generated.java", foundNullable);
+    }
+}
diff --git a/support/src/test/java/com/shopify/graphql/support/Generated.java b/support/src/test/java/com/shopify/graphql/support/Generated.java
index 726b41b..3ae9cf7 100644
--- a/support/src/test/java/com/shopify/graphql/support/Generated.java
+++ b/support/src/test/java/com/shopify/graphql/support/Generated.java
@@ -15,6 +15,8 @@
 
 import com.shopify.graphql.support.ID;
 
+import com.shopify.graphql.support.Nullable;
+
 import java.time.LocalDateTime;
 
 import java.io.Serializable;
@@ -216,6 +218,7 @@ public UnknownEntry setKey(String arg) {
             return this;
         }
 
+        @Nullable
         public LocalDateTime getTtl() {
             return (LocalDateTime) get("ttl");
         }
@@ -398,6 +401,7 @@ public IntegerEntry setKey(String arg) {
             return this;
         }
 
+        @Nullable
         public LocalDateTime getTtl() {
             return (LocalDateTime) get("ttl");
         }
@@ -429,6 +433,9 @@ public boolean unwrapsToObject(String key) {
         }
     }
 
+    /**
+    * Types of values that can be stored in a key
+    */
     public enum KeyType {
         INTEGER,
 
@@ -676,6 +683,9 @@ public QueryRootQuery entries(int first, EntriesArgumentsDefinition argsDef, Ent
             return this;
         }
 
+        /**
+        * Get an entry of any type with the given key
+        */
         public QueryRootQuery entry(String key, EntryQueryDefinition queryDef) {
             startField("entry");
 
@@ -691,6 +701,9 @@ public QueryRootQuery entry(String key, EntryQueryDefinition queryDef) {
             return this;
         }
 
+        /**
+        * Get an entry of any type with the given key as a union
+        */
         public QueryRootQuery entryUnion(String key, EntryUnionQueryDefinition queryDef) {
             startField("entry_union");
 
@@ -706,6 +719,9 @@ public QueryRootQuery entryUnion(String key, EntryUnionQueryDefinition queryDef)
             return this;
         }
 
+        /**
+        * Get a integer value with the given key
+        */
         public QueryRootQuery integer(String key) {
             startField("integer");
 
@@ -760,6 +776,9 @@ public QueryRootQuery keys(int first, KeysArgumentsDefinition argsDef) {
             return this;
         }
 
+        /**
+        * Get a string value with the given key
+        */
         public QueryRootQuery string(String key) {
             startField("string");
 
@@ -936,6 +955,10 @@ public QueryRoot setEntries(List<Entry> arg) {
             return this;
         }
 
+        /**
+        * Get an entry of any type with the given key
+        */
+        @Nullable
         public Entry getEntry() {
             return (Entry) get("entry");
         }
@@ -945,6 +968,10 @@ public QueryRoot setEntry(Entry arg) {
             return this;
         }
 
+        /**
+        * Get an entry of any type with the given key as a union
+        */
+        @Nullable
         public EntryUnion getEntryUnion() {
             return (EntryUnion) get("entry_union");
         }
@@ -954,6 +981,10 @@ public QueryRoot setEntryUnion(EntryUnion arg) {
             return this;
         }
 
+        /**
+        * Get a integer value with the given key
+        */
+        @Nullable
         public Integer getInteger() {
             return (Integer) get("integer");
         }
@@ -972,6 +1003,10 @@ public QueryRoot setKeys(List<String> arg) {
             return this;
         }
 
+        /**
+        * Get a string value with the given key
+        */
+        @Nullable
         public String getString() {
             return (String) get("string");
         }
@@ -981,6 +1016,7 @@ public QueryRoot setString(String arg) {
             return this;
         }
 
+        @Nullable
         public LocalDateTime getTtl() {
             return (LocalDateTime) get("ttl");
         }
@@ -990,6 +1026,7 @@ public QueryRoot setTtl(LocalDateTime arg) {
             return this;
         }
 
+        @Nullable
         public KeyType getType() {
             return (KeyType) get("type");
         }
@@ -999,6 +1036,7 @@ public QueryRoot setType(KeyType arg) {
             return this;
         }
 
+        @Nullable
         public String getVersion() {
             return (String) get("version");
         }
@@ -1039,8 +1077,13 @@ public static class SetIntegerInput implements Serializable {
         private int value;
 
         private LocalDateTime ttl;
+        private boolean ttlSeen = false;
 
         private Boolean negate;
+        private boolean negateSeen = false;
+
+        private String apiClient;
+        private boolean apiClientSeen = false;
 
         public SetIntegerInput(String key, int value) {
             this.key = key;
@@ -1066,21 +1109,36 @@ public SetIntegerInput setValue(int value) {
             return this;
         }
 
+        @Nullable
         public LocalDateTime getTtl() {
             return ttl;
         }
 
-        public SetIntegerInput setTtl(LocalDateTime ttl) {
+        public SetIntegerInput setTtl(@Nullable LocalDateTime ttl) {
             this.ttl = ttl;
+            this.ttlSeen = true;
             return this;
         }
 
+        @Nullable
         public Boolean getNegate() {
             return negate;
         }
 
-        public SetIntegerInput setNegate(Boolean negate) {
+        public SetIntegerInput setNegate(@Nullable Boolean negate) {
             this.negate = negate;
+            this.negateSeen = true;
+            return this;
+        }
+
+        @Nullable
+        public String getApiClient() {
+            return apiClient;
+        }
+
+        public SetIntegerInput setApiClient(@Nullable String apiClient) {
+            this.apiClient = apiClient;
+            this.apiClientSeen = true;
             return this;
         }
 
@@ -1098,18 +1156,37 @@ public void appendTo(StringBuilder _queryBuilder) {
             _queryBuilder.append("value:");
             _queryBuilder.append(value);
 
-            if (ttl != null) {
+            if (this.ttlSeen) {
                 _queryBuilder.append(separator);
                 separator = ",";
                 _queryBuilder.append("ttl:");
-                Query.appendQuotedString(_queryBuilder, ttl.toString());
+                if (ttl != null) {
+                    Query.appendQuotedString(_queryBuilder, ttl.toString());
+                } else {
+                    _queryBuilder.append("null");
+                }
             }
 
-            if (negate != null) {
+            if (this.negateSeen) {
                 _queryBuilder.append(separator);
                 separator = ",";
                 _queryBuilder.append("negate:");
-                _queryBuilder.append(negate);
+                if (negate != null) {
+                    _queryBuilder.append(negate);
+                } else {
+                    _queryBuilder.append("null");
+                }
+            }
+
+            if (this.apiClientSeen) {
+                _queryBuilder.append(separator);
+                separator = ",";
+                _queryBuilder.append("api_client:");
+                if (apiClient != null) {
+                    Query.appendQuotedString(_queryBuilder, apiClient.toString());
+                } else {
+                    _queryBuilder.append("null");
+                }
             }
 
             _queryBuilder.append('}');
@@ -1200,6 +1277,7 @@ public StringEntry setKey(String arg) {
             return this;
         }
 
+        @Nullable
         public LocalDateTime getTtl() {
             return (LocalDateTime) get("ttl");
         }
diff --git a/support/src/test/java/com/shopify/graphql/support/IntegrationTest.java b/support/src/test/java/com/shopify/graphql/support/IntegrationTest.java
index 3115cab..0ea10d7 100644
--- a/support/src/test/java/com/shopify/graphql/support/IntegrationTest.java
+++ b/support/src/test/java/com/shopify/graphql/support/IntegrationTest.java
@@ -156,4 +156,12 @@ public void testMutationResponse() throws Exception {
         Generated.Mutation data = Generated.MutationResponse.fromJson(json).getData();
         assertEquals(true, data.getSetString().booleanValue());
     }
+
+    @Test
+    public void testOptionalFieldOnInput() throws Exception {
+        String queryString = Generated.mutation(mutation -> mutation
+            .setInteger(new Generated.SetIntegerInput("answer", 42).setTtl(null))
+        ).toString();
+        assertEquals("mutation{set_integer(input:{key:\"answer\",value:42,ttl:null})}", queryString);
+    }
 }