diff --git a/src/main/java/matrix/Matrix.java b/src/main/java/matrix/Matrix.java
index 3a797735bbb392d0a0e3165bd4faaad2aa8608c9..f2c908e63e1e44a2552bbf98a946fba6ba6bee6b 100644
--- a/src/main/java/matrix/Matrix.java
+++ b/src/main/java/matrix/Matrix.java
@@ -57,7 +57,9 @@ public interface Matrix<T> extends Iterable<T> {
     this.set(coordinate.x(), coordinate.y(), newValue);
   }
 
-  Matrix<T> subMatrix(Coordinate corner, int width, int height);
+  default Matrix<T> subMatrix(Coordinate corner, int width, int height){
+    return null ;
+  }
 
 
   /**