Does it sort of look like
this?
I don't know that the "intent" defense will work. Specific intent is to have the knife in your possession. Unless you can show that you didn't know you had it, I suspect that defense will not help.
I would look into the exact wording of the
law you are being charged with violating. If the statute I linked to (which prohibits the carrying of "bayonets, swords, daggers, spears and spearheads") is it, an additional problem is that specific fine-tuning of what is legal and what isn't seems to be delegated to "the Minister", by "notification in the
Gazette." It could be, for example, that a training knife is not covered.
This article suggests that, but unfortunately doesn't mention Singapore specifically.
"Butterfly knife trainers feature a special blunt and unsharpened "blade", and are legal in areas where butterfly knives are not."