[SPARK-26383][CORE] NPE when use DataFrameReader.jdbc with wrong URL

### What changes were proposed in this pull request?
When passing wrong url to jdbc then It would throw IllegalArgumentException instead of NPE.
### How was this patch tested?
Adding test case to Existing tests in JDBCSuite

Closes #23464 from ayudovin/fixing-npe.

Authored-by: ayudovin <a.yudovin6695@gmail.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala

@@ -48,6 +48,7 @@ object JdbcUtils extends Logging {
    * Returns a factory for creating connections to the given JDBC URL.
    *
    * @param options - JDBC options that contains url, table and other information.
+   * @throws IllegalArgumentException if the driver could not open a JDBC connection.
    */
   def createConnectionFactory(options: JDBCOptions): () => Connection = {
     val driverClass: String = options.driverClass
@@ -60,7 +61,11 @@ object JdbcUtils extends Logging {
         throw new IllegalStateException(
           s"Did not find registered driver with class $driverClass")
       }
-      driver.connect(options.url, options.asConnectionProperties)
+      val connection: Connection = driver.connect(options.url, options.asConnectionProperties)
+      require(connection != null,
+        s"The driver could not open a JDBC connection. Check the URL: ${options.url}")
+
+      connection
     }
   }
 

sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala

@@ -1507,4 +1507,17 @@ class JDBCSuite extends QueryTest
       checkNotPushdown(sql("SELECT name, theid FROM predicateOption WHERE theid = 1")),
       Row("fred", 1) :: Nil)
   }
+
+  test("SPARK-26383 throw IllegalArgumentException if wrong kind of driver to the given url") {
+    val e = intercept[IllegalArgumentException] {
+      val opts = Map(
+        "url" -> "jdbc:mysql://localhost/db",
+        "dbtable" -> "table",
+        "driver" -> "org.postgresql.Driver"
+      )
+      spark.read.format("jdbc").options(opts).load
+    }.getMessage
+    assert(e.contains("The driver could not open a JDBC connection. " +
+      "Check the URL: jdbc:mysql://localhost/db"))
+  }
 }