how to add more data from extension table to tt_news template using genericmarkers

I am trying to add a reference to a tt_news entry by using the following typoscript code:

plugin.tt_news.genericmarkers {
    data = tx_extendednews_referenz

    REFERENZ = CONTENT
    REFERENZ {

        table = tx_referenzen
        select {
            pidInList = 8
            selectFields = tx_referenzen.title
            andWhere.dataWrap = tx_referenzen.uid = {field:generic_tx_extendednews_referenz}
        }
        renderObj = COA
        renderObj {
            10 = TEXT
            10.field = title
        }
    }
}

The ###GENERIC_REFERENZ### marker shows the title of the corresponding reference, so it seems like it works. but there is this typo3 error message in the header of the page saying I have an error in my SQL syntax. The lastBuiltQuery looks like this:

SELECT tx_referenzen.title, tx_referenzen.uid as uid, tx_referenzen.pid as pid FROM tx_referenzen WHERE tx_referenzen.pid IN (8) AND tx_referenzen.uid = AND tx_referenzen.deleted=0 AND tx_referenzen.hidden=0

So there is the corresponding reference uid missing in the query, that came with the andWhere in the typoscript code. i am wondering, why it is missing in the query, though on the page the correct reference title shows up.

When I just reload (strg+r) the page, the error message disappears, but when I press strg+shift+r, it comes back. What is wrong with the typoscript? Any ideas?

update:

I changed the select-statement to:

    select {
        pidInList = 8
        selectFields = tx_referenzen.title, tx_referenzen.uid
        andWhere {
            dataWrap = tx_referenzen.uid = {field:generic_tx_extendednews_referenz}
            if.isTrue.data = field:generic_tx_extendednews_referenz
            if.isTrue.data.ifEmpty = 1
        }
    }

Now it seems to work in the first place. The error message is gone and it shows the corresponding reference with the news entry. but: Now if there is no reference added to the news-entry, all of the references are listed next to the news entry instead of none. So I have to change my question to: how do I change the typoscript so that it only lists references if there are any added to a news entry?

This would be my solution:

data = tx_extendednews_referenz

1 = LOAD_REGISTER
1.param.cObject = TEXT
1.param.cObject.value = 0
1.param.cObject.override.data = field:generic_tx_extendednews_referenz

REFERENZ = CONTENT
REFERENZ {

    table = tx_referenzen
    select {
        pidInList = 8
        selectFields = tx_referenzen.title, tx_referenzen.images, tx_referenzen.uid
        andWhere =  tx_referenzen.uid = {REGISTER:param}
        andWhere.insertData = 1
    }

it defines a default value of 0 in the register and if your field is not empty this default value is overwritten by the field-value.