diff --git a/src/graphql/query-builder.ts b/src/graphql/query-builder.ts
index c0c0c25..7404299 100644
--- a/src/graphql/query-builder.ts
+++ b/src/graphql/query-builder.ts
@@ -1,4 +1,5 @@
 import {EnumType, jsonToGraphQLQuery} from 'json-to-graphql-query';
+import {isNil} from 'lodash';
 
 import {ConflictClause, Mutation, MutationObject} from './types';
 
@@ -8,7 +9,9 @@ type MutationFieldValue =
   | boolean
   | any[]
   | {category: string; detail: string}
-  | Ref;
+  | Ref
+  | undefined
+  | null;
 
 interface MutationFields {
   [field: string]: MutationFieldValue;
@@ -57,13 +60,14 @@ export class QueryBuilder {
    */
   private mutationObj(model: FarosModel, ref = false): MutationObject {
     const [modelName, fields] = Object.entries(model)[0];
-    const cleanObj = removeUndefinedProperties(fields ?? {});
     const mutObj: any = {};
     const mask = ['refreshedAt'];
 
-    for (const [k, v] of Object.entries(cleanObj)) {
+    for (const [k, v] of Object.entries(fields ?? {})) {
       let maskKey = k;
-      if (v instanceof Ref) {
+      if (isNil(v)) {
+        mutObj[k] = null;
+      } else if (v instanceof Ref) {
         mutObj[k] = this.mutationObj(v.model, true);
         // ref's key should be suffixed with Id for onConflict field
         maskKey += 'Id';
@@ -112,15 +116,7 @@ export class QueryBuilder {
 }
 
 export function mask(object: any): string[] {
-  return Object.keys(removeUndefinedProperties(object));
-}
-
-function removeUndefinedProperties(object: MutationFields): MutationFields {
-  const result = {...object};
-  Object.keys(result).forEach(
-    (key) => result[key] === undefined && delete result[key]
-  );
-  return result;
+  return Object.keys(object);
 }
 
 /**
diff --git a/test/__snapshots__/query-builder.test.ts.snap b/test/__snapshots__/query-builder.test.ts.snap
index e32ac4d..adeaeb0 100644
--- a/test/__snapshots__/query-builder.test.ts.snap
+++ b/test/__snapshots__/query-builder.test.ts.snap
@@ -3,3 +3,5 @@
 exports[`query builder creates mutations 1`] = `"mutation { m0: insert_compute_Application_one (object: {name: \\"<application_name>\\", platform: \\"<application_platform>\\", origin: \\"test-origin\\"}, on_conflict: {constraint: compute_Application_pkey, update_columns: [refreshedAt, name, platform, origin]}) { id } m1: insert_cicd_Organization_one (object: {uid: \\"<organization_uid>\\", source: \\"<organization_source>\\", origin: \\"test-origin\\"}, on_conflict: {constraint: cicd_Organization_pkey, update_columns: [refreshedAt, uid, source, origin]}) { id } m2: insert_cicd_Pipeline_one (object: {uid: \\"<pipeline_uid>\\", organization: {data: {uid: \\"<organization_uid>\\", source: \\"<organization_source>\\"}, on_conflict: {constraint: cicd_Organization_pkey, update_columns: [refreshedAt]}}, origin: \\"test-origin\\"}, on_conflict: {constraint: cicd_Pipeline_pkey, update_columns: [refreshedAt, uid, organizationId, origin]}) { id } m3: insert_cicd_Build_one (object: {uid: \\"<cicd_Build>\\", pipeline: {data: {uid: \\"<pipeline_uid>\\", organization: {data: {uid: \\"<organization_uid>\\", source: \\"<organization_source>\\"}, on_conflict: {constraint: cicd_Organization_pkey, update_columns: [refreshedAt]}}}, on_conflict: {constraint: cicd_Pipeline_pkey, update_columns: [refreshedAt]}}, name: \\"<build_name>\\", origin: \\"test-origin\\"}, on_conflict: {constraint: cicd_Build_pkey, update_columns: [refreshedAt, uid, pipelineId, name, origin]}) { id } m4: insert_cicd_Deployment_one (object: {uid: \\"<deployment_uid\\", source: \\"<deployment_source>\\", application: {data: {name: \\"<application_name>\\", platform: \\"<application_platform>\\"}, on_conflict: {constraint: compute_Application_pkey, update_columns: [refreshedAt]}}, build: {data: {uid: \\"<cicd_Build>\\", pipeline: {data: {uid: \\"<pipeline_uid>\\", organization: {data: {uid: \\"<organization_uid>\\", source: \\"<organization_source>\\"}, on_conflict: {constraint: cicd_Organization_pkey, update_columns: [refreshedAt]}}}, on_conflict: {constraint: cicd_Pipeline_pkey, update_columns: [refreshedAt]}}, name: \\"<build_name>\\"}, on_conflict: {constraint: cicd_Build_pkey, update_columns: [refreshedAt]}}, status: {category: \\"Success\\", detail: \\"<status_detail>\\"}, origin: \\"test-origin\\"}, on_conflict: {constraint: cicd_Deployment_pkey, update_columns: [refreshedAt, uid, source, applicationId, buildId, status, origin]}) { id } }"`;
 
 exports[`query builder creates mutations with non-model objects 1`] = `"mutation { m0: insert_qa_TestCase_one (object: {uid: \\"<uid>\\", source: \\"<source>\\", name: \\"<name>\\", before: [{description: \\"<description>\\", condition: \\"<condition>\\"}], after: [{description: \\"<description>\\", condition: \\"<condition>\\"}], tags: \\"{tag1,tag2}\\", origin: \\"test-origin\\"}, on_conflict: {constraint: qa_TestCase_pkey, update_columns: [refreshedAt, uid, source, name, before, after, tags, origin]}) { id } }"`;
+
+exports[`query builder creates mutations with undefined and null fields 1`] = `"mutation { m0: insert_qa_TestCase_one (object: {uid: \\"<uid>\\", source: \\"<source>\\", name: \\"<name>\\", before: null, after: null, tags: \\"{tag1,tag2}\\", origin: \\"test-origin\\"}, on_conflict: {constraint: qa_TestCase_pkey, update_columns: [refreshedAt, uid, source, name, before, after, tags, origin]}) { id } }"`;
diff --git a/test/query-builder.test.ts b/test/query-builder.test.ts
index ca34b1e..c0887cb 100644
--- a/test/query-builder.test.ts
+++ b/test/query-builder.test.ts
@@ -61,4 +61,21 @@ describe('query builder', () => {
     const queryString = sut.batchMutation(mutations);
     expect(queryString).toMatchSnapshot();
   });
+
+  test('creates mutations with undefined and null fields', () => {
+    const qb = new sut.QueryBuilder(ORIGIN);
+
+    const qa_TestCase = {
+      uid: '<uid>',
+      source: '<source>',
+      name: '<name>',
+      before: null,
+      after: undefined,
+      tags: ['tag1', 'tag2'],
+    };
+
+    const mutations = [qb.upsert({qa_TestCase})];
+    const queryString = sut.batchMutation(mutations);
+    expect(queryString).toMatchSnapshot();
+  });
 });