BAEL-1645 fix

spring-5/src/main/java/com/baeldung/assertions/Car.java

@@ -43,6 +43,11 @@ public class Car {
         Assert.isNull(oil, "oil must be null");
         // ...
     }
+    
+    public void replaceBattery(CarBattery carBattery){
+        Assert.isNull(carBattery.getCharge(), "to replace battery the charge must be null");
+        // ...
+    }
 
     public void сhangeEngine(Engine engine) {
         Assert.isInstanceOf(ToyotaEngine.class, engine);

spring-5/src/main/java/com/baeldung/assertions/CarBattery.java

@@ -0,0 +1,13 @@
+package com.baeldung.assertions;
+
+public class CarBattery {
+    private String charge;
+
+    public String getCharge() {
+        return charge;
+    }
+
+    public void setCharge(String charge) {
+        this.charge = charge;
+    }
+}