Resolve "Die Statistiken sollten auch in ElasticSearch hinterlegt werden."

Related to #384 (closed)

src/main/java/at/ac/uibk/gitsearch/es/model/ArtemisExerciseInfo.java

@@ -3,6 +3,7 @@ package at.ac.uibk.gitsearch.es.model;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 import java.util.Objects;
+import org.apache.commons.lang3.StringUtils;
 
 @JsonIgnoreProperties(ignoreUnknown = true)
 @SuppressWarnings("PMD")
@@ -104,10 +105,10 @@ public class ArtemisExerciseInfo extends ExerciseInfo {
         }
         exerciseInfo.setCreator(this.getCreator());
         exerciseInfo.setDescription(this.getDescription());
-        if (this.getDifficulty() != null) {
-            exerciseInfo.setDifficulty(this.getDifficulty());
+        if (StringUtils.isEmpty(this.getDifficulty())) {
+            exerciseInfo.setDifficulty(null);
         } else {
-            exerciseInfo.setDifficulty("medium");
+            exerciseInfo.setDifficulty(this.getDifficulty());
         }
         if (this.getEducationalAlignment() != null) {
             exerciseInfo.setEducationalAlignment(this.getEducationalAlignment());