Fix support to set a custom database name in Host-less JDBC urls

modules/jdbc/src/main/java/org/testcontainers/jdbc/ConnectionUrl.java

@@ -107,7 +107,7 @@ private void parseUrl() {
         //In case it matches to the default pattern
         Matcher dbInstanceMatcher = Patterns.DB_INSTANCE_MATCHING_PATTERN.matcher(dbHostString);
         if (dbInstanceMatcher.matches()) {
-            databaseHost = Optional.of(dbInstanceMatcher.group("databaseHost"));
+            databaseHost = Optional.ofNullable(dbInstanceMatcher.group("databaseHost"));
             databasePort = Optional.ofNullable(dbInstanceMatcher.group("databasePort")).map(Integer::valueOf);
             databaseName = Optional.of(dbInstanceMatcher.group("databaseName"));
         }
@@ -227,7 +227,7 @@ public interface Patterns {
 
         //Matches to part of string - hostname:port/databasename
         Pattern DB_INSTANCE_MATCHING_PATTERN = Pattern.compile(
-            "(?<databaseHost>[^:]+)" +
+            "(?<databaseHost>[^:]+)?" +
             "(:(?<databasePort>[0-9]+))?" +
             "(" +
             "(?<sidOrServiceName>[:/])" +

modules/jdbc/src/test/java/org/testcontainers/jdbc/ConnectionUrlTest.java

@@ -111,4 +111,20 @@ public void testDaemonCapture() {
 
         assertThat(url.isInDaemonMode()).as("Daemon flag is set to true.").isTrue();
     }
+
+    @Test
+    public void testHostLessConnectionUrl() {
+        String urlString = "jdbc:tc:mysql:8.0.36:///databasename?a=b&c=d";
+        ConnectionUrl url = ConnectionUrl.newInstance(urlString);
+
+        assertThat(url.getDatabaseType()).as("Database Type value is as expected").isEqualTo("mysql");
+        assertThat(url.getImageTag()).as("Database Image tag value is as expected").contains("8.0.36");
+        assertThat(url.getQueryString()).as("Query String value is as expected").contains("?a=b&c=d");
+        assertThat(url.getDatabaseHost()).as("Database Host value is as expected").isEmpty();
+        assertThat(url.getDatabasePort()).as("Database Port value is as expected").isEmpty();
+        assertThat(url.getDatabaseName()).as("Database Name value is as expected").contains("databasename");
+
+        assertThat(url.getQueryParameters()).as("Parameter a is captured").containsEntry("a", "b");
+        assertThat(url.getQueryParameters()).as("Parameter c is captured").containsEntry("c", "d");
+    }
 }