feat : Null pointer exception and program crash when configuration values are not given in the yml file

sources/payment-hub/pom.xml

@@ -149,6 +149,25 @@
             <artifactId>interop-ilp-conditions</artifactId>
             <version>1.3</version>
         </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-test</artifactId>
+            <version>5.1.2.RELEASE</version>
+            <scope>compile</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-test</artifactId>
+        </dependency>
     </dependencies>
 
     <dependencyManagement>

sources/payment-hub/src/main/java/hu/HubSettingsTest.java

@@ -0,0 +1,44 @@
+package hu;
+
+import hu.dpc.rt.psp.config.HubSettings;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.junit.Assert.*;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(classes = { HubSettingsTest.TestConfiguration.class })
+public class HubSettingsTest {
+
+    @Autowired
+    private HubSettings hubSettings;
+
+    @Test
+    public void getInstance() {
+        assertEquals("in01",hubSettings.getInstance());
+    }
+
+    @Test
+    public void getExpiration() {
+        assertEquals("30000",hubSettings.getExpiration().toString());
+    }
+
+    @Test
+    public void getTenants_0() {
+        assertEquals("tn03",hubSettings.getTenants().get(0));
+    }
+
+    @Test
+    public void getTenants_1() {
+        assertEquals("tn04",hubSettings.getTenants().get(1));
+    }
+
+    @EnableConfigurationProperties(HubSettings.class)
+    public static class TestConfiguration {
+        // nothing
+    }
+}