Fixes some warnings

Author: Sebastian Krieter

src/main/java/de/vill/conversion/ConvertTypeLevel.java

@@ -3,7 +3,6 @@
 import de.vill.model.Attribute;
 import de.vill.model.Feature;
 import de.vill.model.FeatureModel;
-import de.vill.model.FeatureType;
 import de.vill.model.Group;
 import de.vill.model.LanguageLevel;
 import de.vill.model.constraint.Constraint;

src/main/java/de/vill/main/Example.java

@@ -29,15 +29,15 @@ public static void main(String[] args) throws IOException {
             traverseConstraint(ownConstraint.get(0));
         }
 
-        //get all constraints of feature model and submodels and attribtues
+        //get all constraints of feature model and submodels and attributes
         List<Constraint> allConstraint = featureModel.getConstraints();
 
         //get attribute from feature
         String featureName = "featureName";
         String attributeName = "attributeName";
         Feature feature = featureModel.getFeatureMap().get(featureName);
         if (feature != null) {
-            Attribute attribute = feature.getAttributes().get(attributeName);
+            Attribute<?> attribute = feature.getAttributes().get(attributeName);
             if (attribute != null) {
                 Object value = attribute.getValue();
                 System.out.println("Attribute " + attributeName + " of feature " + featureName + " is: " + value.toString());

src/main/java/de/vill/model/expression/LiteralExpression.java

@@ -48,7 +48,7 @@ public String getFeatureName() {
         return this.featureName;
     }
 
-    public Attribute getAttribute() {
+    public Attribute<?> getAttribute() {
         if (this.feature == null) {
             return null;
         }

src/main/java/de/vill/model/expression/SumAggregateFunctionExpression.java

@@ -1,7 +1,6 @@
 package de.vill.model.expression;
 
 import de.vill.util.Constants;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 

src/test/java/de/vill/model/FeatureTest.java

@@ -3,7 +3,6 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import de.vill.model.Group;
 import de.vill.model.Group.GroupType;
 
 import java.util.LinkedList;