treat empty property as null

src/main/java/com/zaxxer/hikari/metrics/PoolStats.java

@@ -38,7 +38,7 @@ public abstract class PoolStats
    public PoolStats(final long timeoutMs)
    {
       this.timeoutMs = timeoutMs;
-      this.reloadAt = new AtomicLong(0);
+      this.reloadAt = new AtomicLong();
       this.clock = ClockSource.INSTANCE;
    }
    

src/main/java/com/zaxxer/hikari/pool/PoolBase.java

@@ -67,14 +67,14 @@ abstract class PoolBase
       this.config = config;
 
       this.networkTimeout = -1;
-      this.catalog = config.getCatalog();
+      this.catalog = config.getCatalog() == null || config.getCatalog().isEmpty() ? null : config.getCatalog();
       this.isReadOnly = config.isReadOnly();
       this.isAutoCommit = config.isAutoCommit();
       this.transactionIsolation = UtilityElf.getTransactionIsolation(config.getTransactionIsolation());
 
       this.isQueryTimeoutSupported = UNINITIALIZED;
       this.isNetworkTimeoutSupported = UNINITIALIZED;
-      this.isUseJdbc4Validation = config.getConnectionTestQuery() == null;
+      this.isUseJdbc4Validation = config.getConnectionTestQuery() == null || config.getConnectionTestQuery().isEmpty();
       this.isIsolateInternalQueries = config.isIsolateInternalQueries();
 
       this.poolName = config.getPoolName();

src/main/java/com/zaxxer/hikari/util/ConcurrentBag.java

@@ -94,7 +94,7 @@ public class ConcurrentBag<T extends IConcurrentBagEntry> implements AutoCloseab
       this.listener = listener;
       this.weakThreadLocals = useWeakThreadLocals();
 
-      this.waiters = new AtomicInteger(0);
+      this.waiters = new AtomicInteger();
       this.sharedList = new CopyOnWriteArrayList<>();
       this.synchronizer = new QueuedSequenceSynchronizer();
       if (weakThreadLocals) {

src/main/java/com/zaxxer/hikari/util/UtilityElf.java

@@ -115,7 +115,7 @@ public final class UtilityElf
     */
    public static int getTransactionIsolation(final String transactionIsolationName)
    {
-      if (transactionIsolationName != null) {
+      if (transactionIsolationName != null && !transactionIsolationName.isEmpty()) {
          try {
             final String upperName = transactionIsolationName.toUpperCase();
             if (upperName.startsWith("TRANSACTION_")) {