SingleUserGroup: Use AccountCache#getOrNull instead of AccountCache#get

If an account doesn't exist AccountCache#get returns an empty
AccountState instance to represent the missing account. We don't need
single user groups for missing accounts, hence use
AccountCache#getOrNull instead.

Change-Id: Ie6b1073979bc26c8f960fb01cf63ade79d60f4d4
Signed-off-by: Edwin Kempin <ekempin@google.com>

src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
index c2869b2..327849d 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
@@ -106,7 +106,7 @@
     String ident = username(uuid);
     Optional<AccountState> state;
     if (ident.matches(ACCOUNT_ID_PATTERN)) {
-      state = Optional.of(accountCache.get(new Account.Id(Integer.parseInt(ident))));
+      state = Optional.ofNullable(accountCache.getOrNull(new Account.Id(Integer.parseInt(ident))));
     } else if (ident.matches(Account.USER_NAME_PATTERN)) {
       state = accountCache.getByUsername(ident);
     } else {