Hultin’s thesis turns on the reference to salt in Colossians (commanded) and the word eutrapelia in Ephesians (condemned) refer to the same thing - witty speech.
A few very quick reflections:
First, and obviously, they are different words and so there is not an absolute contradiction.
Secondly, though salt had a usual first century meaning (humour) - it also has a strong Biblical usage that does not mean humour (e.g. the OT reference to the covenant; Matthew 5:13 - You are the salt of the earth). Hultin may deal with this in his book, but I think this is a potential problem for his thesis.
In the question time following his paper, a couple of other interesting suggestions were made:
a. The context can affect the meaning of a word - not to change it totally but still significantly. So, the word eutrapelia follows some fairly negative words - filthiness, foolish talk. There is no real indication that the third word in the series is any different.
b. It could be (and I think this might be the most likely) that when Paul says
verse 3 ‘But sexual immorality and all impurity or covetousness must not even be named among you’ and then continues in verse 4 ‘Let there be no filthiness nor foolish talk nor eutrapelia, which are out of place, but instead let there be thanksgiving’ we are to connect the two. That is, these evil things (sexual immorality, impurity, covetousness) should not appear in our speech - even through the otherwise good speech-form of wit. In other words it is not wit per se that he is condemning but what we might describe as double-entendre. I think that is possible in the Greek and fits the context.
That would mean, of course, that the ESV (‘crude joking’) is a fairly good translation! Our humour - in and of itself a good / neutral thing - must not be used in an inappropriate manner.