Lock lease service should short circuit on unlock

changelog/@unreleased/pr-5072.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: Lock lease service should short circuit on unlock
+  links:
+  - https://github.com/palantir/atlasdb/pull/5072

lock-api/src/main/java/com/palantir/lock/client/LockLeaseService.java

@@ -141,6 +141,9 @@ Set<LockToken> refreshLockLeases(Set<LockToken> uncastedTokens) {
     }
 
     Set<LockToken> unlock(Set<LockToken> tokens) {
+        if (tokens.isEmpty()) {
+            return tokens;
+        }
         Set<LeasedLockToken> leasedLockTokens = leasedTokens(tokens);
         leasedLockTokens.forEach(LeasedLockToken::invalidate);