Change: Consistently apply @Nullable

This annotation was not applied consistently to fields and methods, with
some fields having it and their respective getters missing it and vice
versa. Also fix the one instance where it was applied but formatted
differently than in the rest of the code base.

Change-Id: Ie4436fe64642affad7d775c59b10b6bacc0c4acd
Release-Notes: skip
Forward-Compatible: checked
diff --git a/java/com/google/gerrit/entities/Change.java b/java/com/google/gerrit/entities/Change.java
index fad3aa8..3ad7e03 100644
--- a/java/com/google/gerrit/entities/Change.java
+++ b/java/com/google/gerrit/entities/Change.java
@@ -434,7 +434,7 @@
   private Id changeId;
 
   /** ServerId of the Gerrit instance that has created the change */
-  private String serverId;
+  @Nullable private String serverId;
 
   /** Globally assigned unique identifier of the change */
   private Key changeKey;
@@ -545,7 +545,8 @@
    * ServerId of the Gerrit instance that created the change. It could be null when the change is
    * not fetched from NoteDb but obtained through protobuf deserialisation.
    */
-  public @Nullable String getServerId() {
+  @Nullable
+  public String getServerId() {
     return serverId;
   }
 
@@ -607,6 +608,7 @@
     return originalSubject != null ? originalSubject : subject;
   }
 
+  @Nullable
   public String getOriginalSubjectOrNull() {
     return originalSubject;
   }
@@ -652,6 +654,7 @@
     originalSubject = null;
   }
 
+  @Nullable
   public String getSubmissionId() {
     return submissionId;
   }
@@ -684,6 +687,7 @@
     return isAbandoned() || isMerged();
   }
 
+  @Nullable
   public String getTopic() {
     return topic;
   }
@@ -720,10 +724,12 @@
     this.revertOf = revertOf;
   }
 
+  @Nullable
   public Id getRevertOf() {
     return this.revertOf;
   }
 
+  @Nullable
   public PatchSet.Id getCherryPickOf() {
     return cherryPickOf;
   }