Why does sonar think this expression is always false

In my Java project SonarQube says that an expression is always false. However I cannot see why. This is the code in question:

    BaseException baseException = null;

    for (SpaceInfo i: spaceInfos) {
        try {
            processSingle(i.getSpaceKey(), i.getContentType());
        } catch (BaseException e) {
            baseException = BaseException.chain(baseException, e);
        }
    }

    // Here sonar say that this condition will always evaluate to false. 
    if (baseException != null) {
        throw baseException;
    }

However in my opinion if the processSingle method throws a BaseException then baseException should not be null and therefore the expression should not evaluate to false.

The processSingle method is declared as follows:

private void processSingle(String spaceKey, String contentType) throws BaseException

And there are definitely cases in which the processSingle method will throw a BaseException. So I think that Sonar is mistaken. Or is there something going on here that I am not seeing?

Update:

This is what BaseException.chain() does:

public static BaseException chain (BaseException a, BaseException b) {
    if (a == null) { return b; }
    a.setNextException(b);
    return a;
}

And this is the code of processSingle:

private void processSingle(String spaceKey, String contentType) throws BaseException {
    assert ContentTypes.Page.equals(contentType) || ContentTypes.BlogPost.equals(contentType);

    Content content;
    try {
        content = createEmptyContent(spaceKey, contentType);
    } catch (Exception e) {
        throw new MessageToContentProcessorProcessSingleException(contentType, spaceKey, e);
    }

    BaseException baseException = null;

    try {
        contentCreator.addMetadata(content);

    } catch (BaseException e) {
        baseException = BaseException.chain(baseException, e);
    }

    Pair<List<AttachmentInfo>, FailedToSaveAttachmentException> pair = contentCreator.saveAttachments(messageParser.getContent(), content);
    List<AttachmentInfo> attachments = pair.getLeft();
    baseException = BaseException.chain(baseException, pair.getRight());

    try {
        String html = htmlGenerator.generateHtml(attachments, messageParser.getContent());
        contentCreator.updateBodyOfContent(content, html);
    } catch (BaseException e) {
        baseException = BaseException.chain(baseException, e);
    }

    if (baseException != null) {
        throw new MessageToContentProcessorProcessSingleException(contentType, spaceKey, baseException);
    }
}