Weird behaviour with dialog boxes and variables in Lua script for Lightroom plugin - plugins

Question

I'm writing a Lightroom plugin using the Lightroom SDK/API in the Lua language. I'm new to Lua. I've found a situation where my script only works if a Lightroom dialog box (LrDialogs.message("random message")) is present in one function. Without it the function falls over at a later point claiming a string variable (Image.dr in the last LrDialogs.message) is 'nil' as opposed to the normal value it has when the plugin is working properly. Anyone know what's going wrong? Here's the relevant code segment:
------ read output file for exif and write to LR metadata ------
function parseOutput(outputFilePath)
LrDialogs.message("random message")
local tblOutput = {} --to hold the output exif (1 column table, i.e. an array)
local tblImages = {} --to hold the images and their relevant metadata
for line in io.lines(outputFilePath) do
line = removeWhitespaces(line)
table.insert(tblOutput, line)
end
local str = table.remove(tblOutput) --remove last line in table/file (it's log info, not exif)
tblImages = extractExif(tblOutput) --pick out the exif key/value pairs and add to Image objects
end
function extractExif(tblOutput)
local Image = {} --pseudo object to hold metadata for each image
local tblImages = {}
local blnFlag = false
local intCount = 0
for k,v in pairs(tblOutput) do --iterate through each value in the table
if string.find(v, "^=.+") then
--test if new image other than the first one
if blnFlag == true then
--add Image to tblImages and then clear Image object
table.insert(tblImages, Image)
--Image = {} --don't technically need this
blnFlag = false
--LrDialogs.message("inside blnFlag test")
end
i, j = string.find(v, "/") -- **** MAC ONLY. Back slash for Windows *****
Image.filePath = string.sub(v, i) --returns the file path
Image.name = string.match(v, "([^/]+)$") --return the file name
blnFlag = true
elseif string.find(v, "ISO") ~= nil then
Image.iso = string.match(v, "%a+:(.+)") --get text (i.e value) to right of colon
elseif string.find(v, "Film") ~= nil then
Image.filmSim = string.match(v, "%a+:(.+)")
elseif string.find(v, "Setting") ~= nil then
Image.drMode = string.match(v, "%a+:(.+)")
elseif (string.find(v, "Auto") ~= nil) or (string.find(v, "Development") ~= nil) then
Image.dr = string.match(v, "%a+:(.+)")
else
end
end
LrDialogs.message(Image.name .. Image.iso .. Image.filmSim .. Image.drMode .. Image.dr)
return tblImages
end
function removeWhitespaces(str)
return string.gsub(str, "%s", "")
end