API Query looping and not stopping at null results? Help!

Hello Helpful Query Experts,

I am trying to get data from a particularly troublesome API.  It requires a POST command to get results and hides the total record information in return headers which I have not found a way for Power Query to read.  In order to get all paginated results I’m using this technique below I have had work with other API’s creating a function and then a List.Generate query. 

However, in this case it is getting all the paginated results but keeps creating an endless set of null records.  I had to stop it processing and look at the data (see below) to see what it was doing.  I don’t understand why it is not stopping when it hits null?  Can anyone help me figure out where I went wrong in the query or how to force it to stop when it receives null results? I show a postman result with "[]" which represents a null, right?  

I have been working for weeks to get data from this API and feel like I am so close! 

fTessPage function

(tpage as number)=>

let

                url = "https://tessy.com/tessituraservice/Reporting/Lists/182243/Results",

                body = "OutputSetId=1137&"&"Page="&Number.ToText(tpage),

Source = Json.Document(Web.Contents(url,[Headers = [#"Authorization"="Basic <<encoded>>", #"Content-Type"="application/x-www-form-urlencoded"], Content = Text.ToBinary(body)]))

in

    Source

Query to pull all pages

let

TessListQuery = List.Generate(()=>

[Result = try fTessPage(1) otherwise null, tpage=1],

each [Result]<>null,

each [Result = try fTessPage([tpage]+1) otherwise null, tpage=[tpage]+1],

each [Result]),

#"Converted to Table" = Table.FromList(TessListQuery, Splitter.SplitByNothing(), null, null, ExtraValues.Error)

in

#"Converted to Table"

this is what postman returns when the data is empty.  This is a null, right?  

**table with all the null records it keeps collecting.