Why does accessing FieldInfo.value disable search in info column?

edit

Thanks a lot @johnthacker (sorry, I can't vote, I have less than 15 points :-) )! Checking myFieldInstance for ~= nil solves my problem!

Is there a way to see the errors thrown while searching? How did you see this error?

Ah, I thought that would work but it doesn't. Try this instead, using add_packet_field instead of add, which returns the retrieved value immediately as a second return value (similar to the C dissection proto_tree_add_item_ret_XXX() functions):

function myProto.dissector(buffer, pinfo, tree)
    local myItem
    local makeSearchDoesntWork = true
    local myValue = -1
    myItem, myValue = tree:add_packet_field(myProto.fields.Port, buffer(0, 1), ENC_BIG_ENDIAN)
    local msg = "Search works"
    print(myItem.text)
    if makeSearchDoesntWork then
        if tree ~= nil then
            local myFieldInstance = myField()
            -- This line makes search working (for content that does not depend on myValue):
            if myFieldInstance ~= nil then
                --myValue = myFieldInstance.value
                msg = "value was accessed. Does search work??"
            else
                msg = "myFieldInstance is nil"
            end
        else
            msg = "tree is nil"
        end
    end
    pinfo.cols.info = msg .. " / abcde / " .. myValue
end

BTW, I believe you can still "accept" the answer even without upvoting.

Thanks a lot @johnthacker ! This solves my problem completely and futhermore makes it much easier to access the values. No more need to create the Field's!

local myProto = Proto("myproto", "My Protocol")
myProto.fields.Port = ProtoField.uint8("myproto.port", "Port", base.DEC)
function myProto.dissector(buffer, pinfo, tree)
    local myItem, myValue = tree:add_packet_field(myProto.fields.Port, buffer(0, 1), ENC_BIG_ENDIAN)
    pinfo.cols.info = "abcde / " .. myValue
end
register_postdissector(myProto)