To prevent NPE use pool name for metrics if JDBC URL is not set. (#754)

HikariCP pool can be configured using JDBC URL:
```
HikariConfig config = new HikariConfig();
config.setJdbcUrl("jdbc:mysql://localhost:3306/simpsons");
```
or using data source properties
```
Properties props = new Properties();
props.setProperty("dataSourceClassName", "org.postgresql.ds.PGSimpleDataSource");
props.setProperty("dataSource.serverName", "localhost");
...
HikariConfig config = new HikariConfig(props);
HikariDataSource ds = new HikariDataSource(config)
```

Author: john9x

CHANGES.md

@@ -7,6 +7,7 @@ Release Notes.
 
 * Add the virtual thread executor plugin
 * Fix Conflicts apm-jdk-threadpool-plugin conflicts with apm-jdk-forkjoinpool-plugin
+* Fix NPE in hikaricp-plugin if JDBC URL is not set
 
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/236?closed=1)
 

apm-sniffer/apm-sdk-plugin/hikaricp-3.x-4.x-plugin/src/main/java/org/apache/skywalking/apm/plugin/hikaricp/PoolingSealInterceptor.java

@@ -49,8 +49,13 @@ public void beforeMethod(EnhancedInstance objInst, Method method, Object[] allAr
     public Object afterMethod(EnhancedInstance objInst, Method method, Object[] allArguments, Class<?>[] argumentsTypes, Object ret) throws Throwable {
 
         HikariDataSource hikariDataSource = (HikariDataSource) objInst;
-        ConnectionInfo connectionInfo = URLParser.parser(hikariDataSource.getJdbcUrl());
-        String tagValue = connectionInfo.getDatabaseName() + "_" + connectionInfo.getDatabasePeer();
+        String tagValue;
+        if (hikariDataSource.getJdbcUrl() != null) {
+            ConnectionInfo connectionInfo = URLParser.parser(hikariDataSource.getJdbcUrl());
+            tagValue = connectionInfo.getDatabaseName() + "_" + connectionInfo.getDatabasePeer();
+        } else {
+            tagValue = hikariDataSource.getPoolName();
+        }
         final Map<String, Function<HikariPoolMXBean, Supplier<Double>>> poolMetricMap = getPoolMetrics();
         final Map<String, Function<HikariConfigMXBean, Supplier<Double>>> metricConfigMap = getConfigMetrics();
         poolMetricMap.forEach((key, value) -> MeterFactory.gauge(METER_NAME, value.apply(hikariDataSource.getHikariPoolMXBean()))