Fix after code review

Author: Zhen Li

Neo4j.Driver/Neo4j.Driver/Internal/ConnectionPool.cs

@@ -229,6 +229,7 @@ private Task<IConnection> AcquireAsync()
                 IPooledConnection connection = null;
                 if (!_availableConnections.TryTake(out connection))
                 {
+                    // TODO: make this timer a cancellationToken instead
                     Stopwatch connAcquisitionTimer = new Stopwatch();
                     connAcquisitionTimer.Start();
                     do
@@ -245,6 +246,11 @@ private Task<IConnection> AcquireAsync()
                         }
                     } while (connAcquisitionTimer.ElapsedMilliseconds < _connAcquisitionTimeout.TotalMilliseconds);
                     connAcquisitionTimer.Stop();
+
+                    if (connection == null)
+                    {
+                        throw new ClientException($"Failed to obtain a connection from pool within {_connAcquisitionTimeout}");
+                    }
                 }
 
                 if (!connection.IsOpen || HasBeenIdleForTooLong(connection))

Neo4j.Driver/Neo4j.Driver/Internal/ConnectionPoolSettings.cs

@@ -40,10 +40,6 @@ internal ConnectionPoolSettings(int maxIdleConnectionPoolSize, int maxConnection
             TimeSpan connectionAcquisitionTimeout, TimeSpan connectionIdleTimeout, 
             IStatisticsCollector statisticsCollector=null)
         {
-            Throw.ArgumentNullException.IfNull(maxIdleConnectionPoolSize, nameof(maxIdleConnectionPoolSize));
-            Throw.ArgumentNullException.IfNull(maxConnectionPoolSize, nameof(maxConnectionPoolSize));
-            Throw.ArgumentNullException.IfNull(connectionAcquisitionTimeout, nameof(connectionAcquisitionTimeout));
-            Throw.ArgumentNullException.IfNull(connectionIdleTimeout, nameof(connectionIdleTimeout));
             MaxIdleConnectionPoolSize = maxIdleConnectionPoolSize;
             MaxConnectionPoolSize = maxConnectionPoolSize;
             ConnectionAcquisitionTimeout = connectionAcquisitionTimeout;

Neo4j.Driver/Neo4j.Driver/Internal/ConnectionSettings.cs

@@ -45,9 +45,6 @@ private ConnectionSettings(Uri initialServerUri, IAuthToken authToken,
             IfNull(initialServerUri, nameof(initialServerUri));
             IfNull(authToken, nameof(authToken));
             IfNull(encryptionManager, nameof(encryptionManager));
-            IfNull(connectionTimeout, nameof(connectionTimeout));
-            IfNull(socketKeepAlive, nameof(socketKeepAlive));
-            IfNull(ipv6Enabled, nameof(ipv6Enabled));
 
             InitialServerUri = initialServerUri;
             AuthToken = authToken;

Neo4j.Driver/Neo4j.Driver/V1/GraphDatabase.cs

@@ -15,10 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 using System;
-using System.Collections.Generic;
 using Neo4j.Driver.Internal;
 using Neo4j.Driver.Internal.Routing;
-using static Neo4j.Driver.Internal.ExponentialBackoffRetryLogic;
 
 namespace Neo4j.Driver.V1
 {