[F1N4L]

The params, in this case, is a string. Then you have to convert String in Integer with strval.

Examples:

Search ID with isnull

Код:

if(isnull(params))
{
    // code to return false
}
else // code to return true
{
    if(IsPlayerConected(strval(params)))
    {
        // Player Conected
    }
}

Search ID with sscanf

Код:

new Target;
if(sscanf(params, "i", Target))
{
    // code to return false
}
else // code to return true
{
    if(IsPlayerConected(Target))
    {
        // Player Conected
    }
}