Polish.

ModelSyncProvider @ 619bbf1e

-Subproject commit b198d4633ab67b708a81e399be95596a5b4a0b6c
+Subproject commit 619bbf1efcfee406a134412275928322d9d28e05

src/main/java/org/rosi_project/model_sync/model_join/representation/core/OCLConstraint.java

 package org.rosi_project.model_sync.model_join.representation.core;
 
-import java.util.Objects;
 import javax.annotation.Nonnull;
 
 /**

src/main/java/org/rosi_project/model_sync/model_join/representation/grammar/KeepReferenceExpression.java

@@ -8,6 +8,8 @@ import org.rosi_project.model_sync.model_join.representation.core.AttributePath;
 import org.rosi_project.model_sync.model_join.representation.util.Assert;
 
 // TODO the Xtext grammar also specifies an optional `as reference` part - what does that part do?
+// most likely `as reference` will refer to another type that was already defined in its dedicated
+// join statement.
 
 /**
  * A {@code KeepReferenceExpression} retains links to other instances in the original models. All
@@ -52,13 +54,8 @@ public class KeepReferenceExpression extends KeepExpression {
    */
   public static class KeepReferenceBuilder {
 
-    @Nonnull
     private ReferenceDirection referenceDirection;
-
-    @Nonnull
     private AttributePath attribute;
-
-    @Nonnull
     private AttributePath target;
 
     @Nonnull
@@ -119,8 +116,11 @@ public class KeepReferenceExpression extends KeepExpression {
     }
   }
 
+  /**
+   * Starts the creation process for a new {@code KeepReferenceExpression}.
+   */
   @Nonnull
-  public static KeepReferenceBuilder createNew() {
+  public static KeepReferenceBuilder keep() {
     return new KeepReferenceBuilder();
   }