“Does our law condemn a man without first hearing him to find out what he is doing?”
The leaders had condemned the crowd for not knowing the Law and Nicodemus immediately charges them with the same thing. They were not following their own law which is expressed by Rabbi Eleazer ben Pedath thusly, “Unless a mortal hears the pleas that a man can put forward, he is not able to give judgment.” (Ex. R., XXI. 3)
Note that Nicodemus did not deny Christ, but waited for the exact right time to confess Him and did that in the most effective manner possible. He didn’t try to blast them with the gospel (as he knew it) but interjected just enough salt into the conversation to change the flavor of it. It would be well for us to follow his example.