Check null account full name

isFullMatch() tries to match with account full name, but full name
can be null. This patch fixes NPE when a full name is not set.

Change-Id: I3aa654a5ec2dc314a470d9423dae35047aabea94
(cherry picked from commit 7273a85d6a39044234c2167ea60a1ea0b49086b0)
diff --git a/owners-common/src/main/java/com/vmware/gerrit/owners/common/AccountsImpl.java b/owners-common/src/main/java/com/vmware/gerrit/owners/common/AccountsImpl.java
index e28e8ba..5bafdac 100644
--- a/owners-common/src/main/java/com/vmware/gerrit/owners/common/AccountsImpl.java
+++ b/owners-common/src/main/java/com/vmware/gerrit/owners/common/AccountsImpl.java
@@ -32,6 +32,7 @@
 import com.google.inject.Inject;
 import java.io.IOException;
 import java.util.Collections;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -130,7 +131,9 @@
 
   private boolean isFullMatch(Account.Id id, String nameOrEmail) {
     AccountState account = byId.get(id);
-    return account.getAccount().getFullName().trim().equalsIgnoreCase(nameOrEmail)
+    return Objects.toString(account.getAccount().getFullName(), "")
+            .trim()
+            .equalsIgnoreCase(nameOrEmail)
         || account
             .getExternalIds()
             .stream()