Wrap feedback average calculation in Optional type

src/main/java/de/thm/arsnova/model/Feedback.java

@@ -22,12 +22,12 @@ import de.thm.arsnova.model.serialization.View;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Optional;
 
 /**
  * The feedback values of a single session.
  */
 public class Feedback {
-	private static final double Z_THRESHOLD = 0.1;
 
 	public static final int MIN_FEEDBACK_TYPE = 0;
 	public static final int MAX_FEEDBACK_TYPE = 3;
@@ -52,16 +52,16 @@ public class Feedback {
 		return values;
 	}
 
-	public double getAverage() {
-		final double count = this.getCount();
+	public Optional<Double> getAverage() {
+		final int count = this.getCount();
+		if (count == 0) {
+			return Optional.empty();
+		}
+
 		final double sum = values.get(FEEDBACK_OK) + values.get(FEEDBACK_SLOWER) * 2
 				+ values.get(FEEDBACK_AWAY) * 3;
 
-		if (Math.abs(count) < Z_THRESHOLD) {
-			return 0;
-		}
-
-		return sum / count;
+		return Optional.of(sum / count);
 	}
 
 	public int getCount() {

src/main/java/de/thm/arsnova/service/FeedbackServiceImpl.java

@@ -29,11 +29,7 @@ import org.springframework.context.ApplicationEventPublisherAware;
 import org.springframework.scheduling.annotation.Scheduled;
 import org.springframework.stereotype.Service;
 
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
+import java.util.*;
 
 /**
  * Performs all feedback related operations.
@@ -130,11 +126,7 @@ public class FeedbackServiceImpl implements FeedbackService, ApplicationEventPub
 	@Override
 	public double calculateAverageFeedback(final String roomId) {
 		final Feedback feedback = this.getByRoomId(roomId);
-		if (feedback.getCount() == 0) {
-			throw new NoContentException();
-		}
-
-		return feedback.getAverage();
+		return feedback.getAverage().orElseThrow(NoContentException::new);
 	}
 
 	@Override

src/test/java/de/thm/arsnova/model/FeedbackTest.java

@@ -19,6 +19,8 @@ package de.thm.arsnova.model;
 
 import org.junit.Test;
 
+import java.util.Optional;
+
 import static org.junit.Assert.*;
 
 public class FeedbackTest {
@@ -69,7 +71,7 @@ public class FeedbackTest {
 		Feedback f = new Feedback(1, 0, 0, 1);
 
 		double expected = 1.5;
-		double actual = f.getAverage();
+		double actual = f.getAverage().get();
 
 		assertEquals(expected, actual, 0.01);
 	}
@@ -78,10 +80,9 @@ public class FeedbackTest {
 	public void averageCalculationShouldAvoidDivisionByZero() {
 		Feedback f = new Feedback(0, 0, 0, 0);
 
-		double expected = 0;
-		double actual = f.getAverage();
+		Optional<Double> actual = f.getAverage();
 
-		assertEquals(expected, actual, 0.01);
+		assertFalse(actual.isPresent());
 	}
 
 	@Test