fix(jans-auth-server): corrected npe in response type class

#1087

jans-auth-server/model/src/main/java/io/jans/as/model/common/ResponseType.java

@@ -11,6 +11,7 @@
 import com.fasterxml.jackson.annotation.JsonValue;
 import com.google.common.collect.Lists;
 import io.jans.orm.annotation.AttributeEnum;
+import org.apache.commons.lang3.StringUtils;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -136,6 +137,9 @@ public static List<ResponseType> fromString(String paramList, String separator)
     }
 
     public static boolean isImplicitFlow(String responseTypes) {
+        if (StringUtils.isBlank(responseTypes)) {
+            return false;
+        }
         return !responseTypes.contains("code") && (responseTypes.contains("id_token") || responseTypes.contains("token"));
     }
 

jans-auth-server/model/src/test/java/io/jans/as/model/common/ResponseTypeTest.java

@@ -0,0 +1,34 @@
+package io.jans.as.model.common;
+
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.assertFalse;
+import static org.testng.Assert.assertTrue;
+
+/**
+ * @author Yuriy Zabrovarnyy
+ */
+public class ResponseTypeTest {
+
+
+    @Test
+    public void isImplicitFlow_withNull_shouldReturnFalseWithoutException() {
+        assertFalse(ResponseType.isImplicitFlow(null));
+    }
+
+    @Test
+    public void isImplicitFlow_withBlankValue_shouldReturnFalse() {
+        assertFalse(ResponseType.isImplicitFlow(""));
+    }
+
+    @Test
+    public void isImplicitFlow_withUnknownValue_shouldReturnFalse() {
+        assertFalse(ResponseType.isImplicitFlow("dfs"));
+    }
+
+    @Test
+    public void isImplicitFlow_withTokenAndIdTokenValue_shouldReturnTrue() {
+        assertTrue(ResponseType.isImplicitFlow("token id_token"));
+    }
+}