Fix possible NPE (#8199)

this is a follow-up to #7043

I tried to add a test when that PR was opened:

*
d2c6399a6e

but it doesn't really verify anything, since the NPE is throw/caught and
same behavior occurs

instrumentation/jdbc/library/src/main/java/io/opentelemetry/instrumentation/jdbc/internal/JdbcConnectionUrlParser.java

@@ -53,6 +53,9 @@ public enum JdbcConnectionUrlParser {
         }
 
         String path = uri.getPath();
+        if (path == null) {
+          path = "";
+        }
         if (path.startsWith("/")) {
           path = path.substring(1);
         }