[SH nl50] K2s freeplay

Poker Stars, $0.25/$0.50 No Limit Hold'em Cash, 6 Players
Poker Tools Powered By Holdem Manager - The Ultimate Poker Software Suite.

CO: $38.35 (76.7 bb)
BTN: $48.73 (97.5 bb)
SB: $50.25 (100.5 bb)
Hero (BB): $50 (100 bb)
UTG: $51.27 (102.5 bb)
MP: $79.86 (159.7 bb)

Preflop: Hero is BB with 2 K
2 folds, CO calls $0.50, 2 folds, Hero checks

Flop: ($1.25) 4 K 2 (2 players)
Hero bets $0.89, CO calls $0.89

Turn: ($3.03) J (2 players)
Hero bets $2.50, CO calls $2.50

River: ($8.03) 7 (2 players)
Hero bets $6, CO raises to $15, Hero calls $9

vs unk.
flop/turn betting for value from worse Kx, 42, fd
river fold to raise? I though he can raise busted fd often enough, but until I get any info about him I shouldn't assume that?