diff --git a/package-lock.json b/package-lock.json
index df14ffc..c8127b4 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "frlluc-mocking",
-  "version": "1.0.3",
+  "version": "1.0.4",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index 152f11b..268cee1 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "frlluc-mocking",
-  "version": "1.0.3",
+  "version": "1.0.4",
   "description": "A simple mocking framework targetting TypeScript",
   "main": "./lib/index.js",
   "types": "./lib/index.d.ts",
diff --git a/src/core/mock.interface.ts b/src/core/mock.interface.ts
index b86a59e..97235da 100644
--- a/src/core/mock.interface.ts
+++ b/src/core/mock.interface.ts
@@ -1,5 +1,6 @@
 import { IMockedMethodInfo } from './mocked-method-info.interface';
 import { IMockedPropertyInfo } from './mocked-property-info.interface';
+import { Nullable } from 'frlluc-utils';
 
 /** Represents a mock proxy. */
 export interface IMock<T> {
@@ -12,5 +13,5 @@ export interface IMock<T> {
      * @param memberName subject's member name
      * @returns mocked method or property information store
      * */
-    getMemberInfo(memberName: keyof T): IMockedMethodInfo | IMockedPropertyInfo | null;
+    getMemberInfo(memberName: keyof T): Nullable<IMockedMethodInfo | IMockedPropertyInfo>;
 }
diff --git a/src/core/mock.ts b/src/core/mock.ts
index 218551a..18498c2 100644
--- a/src/core/mock.ts
+++ b/src/core/mock.ts
@@ -3,7 +3,7 @@ import { IMockedMethodInfo } from './mocked-method-info.interface';
 import { IMockedPropertyInfo } from './mocked-property-info.interface';
 import { IInvocationData } from './invocation-data.interface';
 import { IMock } from './mock.interface';
-import { reinterpretCast } from 'frlluc-utils';
+import { reinterpretCast, Nullable } from 'frlluc-utils';
 
 let GLOBAL_INVOCATION_NO = 0;
 
@@ -13,7 +13,7 @@ function createMethodInfo(type: MockedInfoType, data: IInvocationData[]): IMocke
         get count(): number {
             return data.length;
         },
-        getData(no: number): IInvocationData | null {
+        getData(no: number): Nullable<IInvocationData> {
             return data[no] || null;
         },
         clear(): void {
@@ -98,7 +98,7 @@ export function partialMock<T>(subject: T, setup: Partial<T>): IMock<T> {
     const members = new Set<string>();
     const invocationCache: { [id: string]: IMockedMethodInfo | IMockedPropertyInfo } = {};
     const result: any = {
-        getMemberInfo(m: string): IMockedMethodInfo | IMockedPropertyInfo | null {
+        getMemberInfo(m: string): Nullable<IMockedMethodInfo | IMockedPropertyInfo> {
             return invocationCache[m] || null;
         }
     };
diff --git a/src/core/mocked-method-info.interface.ts b/src/core/mocked-method-info.interface.ts
index e58bf10..011a59c 100644
--- a/src/core/mocked-method-info.interface.ts
+++ b/src/core/mocked-method-info.interface.ts
@@ -1,5 +1,6 @@
 import { MockedInfoType } from './mocked-info-type.enum';
 import { IInvocationData } from './invocation-data.interface';
+import { Nullable } from 'frlluc-utils';
 
 /** Stores mocked method information. */
 export interface IMockedMethodInfo {
@@ -12,7 +13,7 @@ export interface IMockedMethodInfo {
      * @param invocationNo invocation's index
      * @returns invocation data
      * */
-    getData(invocationNo: number): IInvocationData | null;
+    getData(invocationNo: number): Nullable<IInvocationData>;
     /** Clears all stored invocation data. */
     clear(): void;
 }
diff --git a/src/core/mocked-property-info.interface.ts b/src/core/mocked-property-info.interface.ts
index d2d7b81..6f24ce8 100644
--- a/src/core/mocked-property-info.interface.ts
+++ b/src/core/mocked-property-info.interface.ts
@@ -1,12 +1,13 @@
 import { MockedInfoType } from './mocked-info-type.enum';
 import { IMockedMethodInfo } from './mocked-method-info.interface';
+import { Nullable } from 'frlluc-utils';
 
 /** Stores mocked property information. */
 export interface IMockedPropertyInfo {
     /** Specifies mocked info type. */
     readonly type: MockedInfoType;
     /** Specifies property's mocked getter information store. */
-    readonly get: IMockedMethodInfo | null;
+    readonly get: Nullable<IMockedMethodInfo>;
     /** Specifies property's mocked setter information store. */
-    readonly set: IMockedMethodInfo | null;
+    readonly set: Nullable<IMockedMethodInfo>;
 }