Problem Can't merge FlowVariable Stacks! (likely a loop problem.)

Hi! Im trying to get the best value of k in KNN. I use something similar to iteration over k values using variables in the K Nearest Neighbor node - #4, but I´m getting “Can’t merge FlowVariable Stacks! (likely a loop problem.)” in KNN node due to the X-Partitioner. I need to use this node.