Simplify logic in GitDownloadCommand

Use fewer else conditions and rely on a single fall through return
null if it is not suitable to produce a command.

Change-Id: I70330af6bbab12d2be4ebe14cb4274d4af3bea01

src/main/java/com/googlesource/gerrit/plugins/download/command/GitDownloadCommand.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/download/command/GitDownloadCommand.java b/src/main/java/com/googlesource/gerrit/plugins/download/command/GitDownloadCommand.java
index eaeb82c..e7a3a04 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/download/command/GitDownloadCommand.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/download/command/GitDownloadCommand.java
@@ -38,22 +38,20 @@
   @Override
   public final String getCommand(DownloadScheme scheme, String project,
       String ref) {
-    if (!commandAllowed) {
-      return null;
-    }
-
-    if (scheme instanceof SshScheme
-        || scheme instanceof HttpScheme
-        || scheme instanceof AnonymousHttpScheme
-        || scheme instanceof GitScheme) {
+    if (commandAllowed && isRecognizedScheme(scheme)) {
       String url = scheme.getUrl(project);
       if (url != null) {
         return getCommand(url, ref);
-      } else
-        return null;
-    } else {
-      return null;
+      }
     }
+    return null;
+  }
+
+  private static boolean isRecognizedScheme(DownloadScheme scheme) {
+    return scheme instanceof SshScheme
+        || scheme instanceof HttpScheme
+        || scheme instanceof AnonymousHttpScheme
+        || scheme instanceof GitScheme;
   }
 
   abstract String getCommand(String url, String ref);