Rebase: Extract a method to find base revision

Using while(false) with break is unidiomatic in Gerrit. Use early
returns from a function instead.

Change-Id: Ib188ca5819b0cbe1b111c1ce49b4095fade0f59f

gerrit-server/src/main/java/com/google/gerrit/server/change/Rebase.java

@@ -88,14 +88,29 @@ public class Rebase implements RestModifyView<RevisionResource, RebaseInput>,
 
     try (Repository repo = repoManager.openRepository(change.getProject());
         RevWalk rw = new RevWalk(repo)) {
-      String baseRev = null;
+      rebaseChange.get().rebase(repo, rw, change, rsrc.getPatchSet().getId(),
-      if (input != null && input.base != null) {
+          rsrc.getUser(), findBaseRev(rw, rsrc, input));
+    } catch (InvalidChangeOperationException e) {
+      throw new ResourceConflictException(e.getMessage());
+    } catch (NoSuchChangeException e) {
+      throw new ResourceNotFoundException(change.getId().toString());
+    }
+
+    return json.format(change.getId());
+  }
+
+  private String findBaseRev(RevWalk rw, RevisionResource rsrc,
+      RebaseInput input) throws AuthException, ResourceConflictException,
+      OrmException, IOException {
+    if (input == null || input.base == null) {
+      return null;
+    }
+
+    Change change = rsrc.getChange();
     String base = input.base.trim();
-        do {
     if (base.equals("")) {
       // remove existing dependency to other patch set
-            baseRev = change.getDest().get();
+      return change.getDest().get();
-            break;
     }
 
     ReviewDb db = dbProvider.get();
@@ -109,7 +124,9 @@ public class Rebase implements RestModifyView<RevisionResource, RebaseInput>,
     }
 
     Change baseChange = db.changes().get(basePatchSet.getId().getParentKey());
-          if (baseChange != null) {
+    if (baseChange == null) {
+      return null;
+    }
     if (!baseChange.getProject().equals(change.getProject())) {
       throw new ResourceConflictException("base change is in wrong project: "
                                           + baseChange.getProject());
@@ -124,20 +141,7 @@ public class Rebase implements RestModifyView<RevisionResource, RebaseInput>,
                                           + " is a descendant of the current "
                                           + " change - recursion not allowed");
     }
-            baseRev = basePatchSet.getRevision().get();
+    return basePatchSet.getRevision().get();
-            break;
-          }
-        } while (false);  // just wanted to use the break statement
-      }
-      rebaseChange.get().rebase(repo, rw, change, rsrc.getPatchSet().getId(),
-          rsrc.getUser(), baseRev);
-    } catch (InvalidChangeOperationException e) {
-      throw new ResourceConflictException(e.getMessage());
-    } catch (NoSuchChangeException e) {
-      throw new ResourceNotFoundException(change.getId().toString());
-    }
-
-    return json.format(change.getId());
   }
 
   private boolean isMergedInto(RevWalk rw, PatchSet base, PatchSet tip)