ContributorAgreementsChecker: Use Java's Objects.requireNonNull

Usage of Preconditions.checkNotNull was replaced with the Java API
in change I1d4a6b342e, but this one was either missed or added later.

Change-Id: I93ec9f3077bbda3737d995032a458e1337abba52
diff --git a/java/com/google/gerrit/server/project/ContributorAgreementsChecker.java b/java/com/google/gerrit/server/project/ContributorAgreementsChecker.java
index 4ed1c0c..8912e31 100644
--- a/java/com/google/gerrit/server/project/ContributorAgreementsChecker.java
+++ b/java/com/google/gerrit/server/project/ContributorAgreementsChecker.java
@@ -15,7 +15,7 @@
 package com.google.gerrit.server.project;
 
 import static com.google.common.base.Preconditions.checkArgument;
-import static com.google.common.base.Preconditions.checkNotNull;
+import static java.util.Objects.requireNonNull;
 
 import com.google.gerrit.common.data.ContributorAgreement;
 import com.google.gerrit.common.data.PermissionRule;
@@ -135,7 +135,7 @@
   }
 
   private boolean projectMatchesAnyPattern(String projectName, List<String> regexes) {
-    checkNotNull(regexes);
+    requireNonNull(regexes);
     checkArgument(!regexes.isEmpty());
     for (String patternString : regexes) {
       Pattern pattern;