GH-1004: [JDBC] Fix NPE in ArrowFlightJdbcDriver#connect​(final String url, final Properties info) (#1005)

## What's Changed
`ArrowFlightJdbcDriver.connect(final String url, final Properties info)`
now properly ignores a null value for `info`, obtaining the properties
solely from the URL.

Closes #1004.

Author: ennuite

flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/ArrowFlightJdbcDriver.java

@@ -75,7 +75,9 @@ public Logger getParentLogger() {
   public ArrowFlightConnection connect(final String url, final Properties info)
       throws SQLException {
     final Properties properties = new Properties(info);
-    properties.putAll(info);
+    if (info != null) {
+      properties.putAll(info);
+    }
 
     if (url != null) {
       final Optional<Map<Object, Object>> maybeProperties = getUrlsArgs(url);

flight/flight-sql-jdbc-core/src/test/java/org/apache/arrow/driver/jdbc/ArrowFlightJdbcDriverTest.java

@@ -201,6 +201,30 @@ public void testConnectWithInsensitiveCasePropertyKeys2() throws Exception {
     }
   }
 
+  /**
+   * Tests whether the {@link ArrowFlightJdbcDriver} can establish a successful connection to the
+   * Arrow Flight client when provided with null properties.
+   */
+  @Test
+  public void testConnectWithNullProperties() throws Exception {
+    final Driver driver = new ArrowFlightJdbcDriver();
+    try (Connection connection =
+        driver.connect(
+            "jdbc:arrow-flight://"
+                + dataSource.getConfig().getHost()
+                + ":"
+                + dataSource.getConfig().getPort()
+                + "?"
+                + "useEncryption=false"
+                + "&user="
+                + dataSource.getConfig().getUser()
+                + "&password="
+                + dataSource.getConfig().getPassword(),
+            null)) {
+      assertTrue(connection.isValid(300));
+    }
+  }
+
   /**
    * Tests whether an exception is thrown upon attempting to connect to a malformed URI.
    *