fixed Java 8 build

pom.xml

@@ -177,6 +177,14 @@
           </execution>
         </executions>
       </plugin>
+        <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <configuration>
+                <source>10</source>
+                <target>10</target>
+            </configuration>
+        </plugin>
     </plugins>
   </build>
 

src/main/java/ch/ethz/seb/sebserver/gbl/util/Utils.java

@@ -169,9 +169,9 @@ public final class Utils {
     }
 
     public static <T extends Enum<T>> Collection<Tuple<String>> createSelectionResource(final Class<T> enumClass) {
-        return Arrays.stream(enumClass.getEnumConstants())
+        return Collections.unmodifiableList(Arrays.stream(enumClass.getEnumConstants())
                 .map(e -> new Tuple<>(e.name(), e.name()))
-                .collect(Collectors.toUnmodifiableList());
+                .collect(Collectors.toList()));
     }
 
     public static Collection<String> getListOfLines(final String list) {