Bug description

When calling RecursiveCollectionLineAggregator.aggregate() with an empty collection, the method throws a StringIndexOutOfBoundsException due to an unguarded StringBuilder.delete(...) call.

Expected behavior

It should return an empty string ("") without throwing an exception.

Minimal Complete Reproducible example

In RecursiveCollectionLineAggregatorTests.class:

@Test
void testSetDelegateAndPassEmptyCollection() {
    RecursiveCollectionLineAggregator<String> aggregator = new RecursiveCollectionLineAggregator<>();
    aggregator.setDelegate(item -> "bar");
    assertEquals("", aggregator.aggregate(Collections.emptyList()));
}

Result: java.lang.StringIndexOutOfBoundsException