this.sources = sources;
    }

    /**
     * Adds a source to the message.
     *
     * @param source the source to add
     */
    public void addSource(final ChatSource source) {
        if (sources == null) {
            sources = new ArrayList<>();
        }
        sources.add(source);
    }

    /**
     * Checks if this is a user message.

        doc1.put("title", "Installation Guide");
        doc1.put("url", "http://example.com/install");
        msg.addSource(new ChatSource(1, doc1));
        final Map<String, Object> doc2 = new HashMap<>();
        doc2.put("title", "Quick Start");
        doc2.put("url", "http://example.com/start");
        msg.addSource(new ChatSource(2, doc2));

        final ChatMessage message = new ChatMessage();
        final ChatSource source = new ChatSource();
        source.setIndex(1);
        source.setTitle("Test Document");

        message.addSource(source);

        assertEquals(1, message.getSources().size());
        assertEquals("Test Document", message.getSources().get(0).getTitle());
    }

    @Test
    public void test_addSourceWithNullSources() {

            final ChatSource source = new ChatSource(i + 1, sourceList.get(i));
            source.setGoUrl(buildGoUrl(contextPath, source.getDocId(), queryId, requestedTime, i));
            assistantMessage.addSource(source);
        }
    }

    /**
     * Populates the url_link field in the document map if not already present.
     *
     * @param doc the document map
     */