diff --git a/packages/sql/src/serializer/sql-serializer.ts b/packages/sql/src/serializer/sql-serializer.ts
index 5ee1dec74..7b70a40c2 100644
--- a/packages/sql/src/serializer/sql-serializer.ts
+++ b/packages/sql/src/serializer/sql-serializer.ts
@@ -93,6 +93,12 @@ function deserializeSqlObjectLiteral(type: TypeClass | TypeObjectLiteral, state:
 export class SqlSerializer extends Serializer {
     name = 'sql';
 
+    override setExplicitUndefined(type: Type, state: TemplateState): boolean {
+        //make sure that `foo?: string` is not explicitly set to undefined when database returns `null`.
+        if (state.target === 'deserialize') return false;
+        return true;
+    }
+
     protected registerSerializers() {
         super.registerSerializers();
 
@@ -104,7 +110,7 @@ export class SqlSerializer extends Serializer {
         const uuidType = uuidAnnotation.registerType({ kind: ReflectionKind.string }, true);
 
         this.deserializeRegistry.register(ReflectionKind.string, (type, state) => {
-            //remove string enforcement, since UUID/MonogId are string but received as binary
+            //remove string enforcement, since UUID/MongoId are string but received as binary
             state.addSetter(state.accessor);
         });
 
diff --git a/packages/sqlite/src/sqlite-adapter.ts b/packages/sqlite/src/sqlite-adapter.ts
index e2611a7b8..7464cde09 100644
--- a/packages/sqlite/src/sqlite-adapter.ts
+++ b/packages/sqlite/src/sqlite-adapter.ts
@@ -11,6 +11,7 @@
 import { AbstractClassType, asyncOperation, ClassType, empty } from '@deepkit/core';
 import {
     DatabaseAdapter,
+    DatabaseError,
     DatabaseLogger,
     DatabasePersistenceChangeSet,
     DatabaseSession,
@@ -515,6 +516,9 @@ export class SQLiteQueryResolver<T extends OrmEntity> extends SQLQueryResolver<T
 
         const sqlBuilder = new SqlBuilder(this.platform, selectParams);
         const selectSQL = sqlBuilder.select(this.classSchema, model, { select });
+        if (!set.length) {
+            throw new DatabaseError('SET is empty');
+        }
 
         const sql = `
               UPDATE
diff --git a/packages/sqlite/tests/sqlite.spec.ts b/packages/sqlite/tests/sqlite.spec.ts
index ced1dfc9d..481415283 100644
--- a/packages/sqlite/tests/sqlite.spec.ts
+++ b/packages/sqlite/tests/sqlite.spec.ts
@@ -4,8 +4,8 @@ import { databaseFactory } from './factory';
 import { User, UserCredentials } from '@deepkit/orm-integration';
 import { SQLiteDatabaseAdapter, SQLiteDatabaseTransaction } from '../src/sqlite-adapter';
 import { sleep } from '@deepkit/core';
-import { AutoIncrement, cast, Entity, entity, PrimaryKey, Reference, ReflectionClass, typeOf } from '@deepkit/type';
-import { DatabaseEntityRegistry } from '@deepkit/orm';
+import { AutoIncrement, cast, Entity, entity, PrimaryKey, Reference, ReflectionClass, serialize, typeOf } from '@deepkit/type';
+import { Database, DatabaseEntityRegistry } from '@deepkit/orm';
 
 test('reflection circular reference', () => {
     const user = ReflectionClass.from(User);
@@ -263,3 +263,24 @@ test('connection pool', async () => {
         expect(c12).toBe(c2);
     }
 });
+
+test('optional', async () => {
+    @entity.name('entity')
+    class MyEntity {
+        id: number & PrimaryKey & AutoIncrement = 0;
+        value?: string;
+    }
+
+    const database = new Database(new SQLiteDatabaseAdapter(), [MyEntity]);
+    await database.migrate();
+
+    const entity1 = new MyEntity();
+    expect('value' in entity1).toBe(false);
+    expect('value' in serialize<MyEntity>(entity1)).toBe(false);
+
+    await database.persist(entity1);
+
+    const entity2 = await database.query(MyEntity).findOne();
+    expect('value' in entity2).toBe(false);
+    expect('value' in serialize<MyEntity>(entity1)).toBe(false);
+});
diff --git a/packages/type/src/serializer.ts b/packages/type/src/serializer.ts
index 14b837bc7..e575fd067 100644
--- a/packages/type/src/serializer.ts
+++ b/packages/type/src/serializer.ts
@@ -42,7 +42,6 @@ import {
     stringifyType,
     Type,
     TypeClass,
-    TypeFunction,
     TypeIndexSignature,
     TypeObjectLiteral,
     TypeParameter,
@@ -725,9 +724,8 @@ export function createConverterJSForMember(
         }
     }
 
-    const optional = isOptional(property instanceof ReflectionProperty ? property.property : property);
+    const setExplicitUndefined = registry.serializer.setExplicitUndefined(type, state) && isOptional(property instanceof ReflectionProperty ? property.property : property);
     const nullable = isNullable(type);
-    // const hasDefault = property instanceof ReflectionProperty ? property.hasDefault() : false;
 
     // // since JSON does not support undefined, we emulate it via using null for serialization, and convert that back to undefined when deserialization happens.
     // // note: When the value is not defined (property.name in object === false), then this code will never run.
@@ -746,7 +744,7 @@ export function createConverterJSForMember(
     //note: this code is only reached when ${accessor} was actually defined checked by the 'in' operator.
     return `
         if (${state.accessor} === undefined) {
-            if (${optional}) {
+            if (${setExplicitUndefined}) {
                 ${undefinedSetterCode}
             }
         } else if (${state.accessor} === null) {
@@ -756,7 +754,7 @@ export function createConverterJSForMember(
             if (${nullable}) {
                 ${nullSetterCode}
             } else {
-                if (${optional}) {
+                if (${setExplicitUndefined}) {
                     ${undefinedSetterCode}
                 }
             }
@@ -1703,6 +1701,10 @@ export class Serializer {
         this.registerValidators();
     }
 
+    public setExplicitUndefined(type: Type, state: TemplateState): boolean {
+        return true;
+    }
+
     protected registerValidators() {
     }
 
diff --git a/packages/type/tests/type-spec.spec.ts b/packages/type/tests/type-spec.spec.ts
index 95c40b969..8411bae7c 100644
--- a/packages/type/tests/type-spec.spec.ts
+++ b/packages/type/tests/type-spec.spec.ts
@@ -95,6 +95,7 @@ test('partial keeps explicitely undefined fields', () => {
 
     {
         const item = serializeToJson<Partial<Model>>({ title: undefined });
+        expect(item).toEqual({ title: null });
     }
 
     {
@@ -755,9 +756,9 @@ test('dynamic properties', () => {
         }
     }
 
-    const back1 = deserializeFromJson<A>({'~type': 'abc'});
+    const back1 = deserializeFromJson<A>({ '~type': 'abc' });
     expect(back1.getType()).toBe('abc');
 
-    const back2 = deserializeFromJson<A>({'type': 'abc'});
+    const back2 = deserializeFromJson<A>({ 'type': 'abc' });
     expect(back2.getType()).toBe('abc');
 });