How to find the rows with missing date range

Here is the solution in Power Query.  For each store code it lists all the days that are not covered by any billing period.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("XY7BDYAwDAN3ybuSnYTSdJaq+68BFRAEz/Pdw2OIShE1sMJoXLCB+wWz3L6CLX0D4+cjpxMc7K+PFVBBfwJnwifIB9YT5jwA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Store code" = _t, #"Bill Start Date" = _t, #"Bill End date" = _t]),
    #"Locale Start Date" = Table.AddColumn(Source, "Start Date", each Date.FromText([Bill Start Date],"en-gb")),
    #"Locale End Date" = Table.AddColumn(#"Locale Start Date", "End Date", each Date.FromText([Bill End date],"en-gb")),
    #"Changed Type" = Table.TransformColumnTypes(#"Locale End Date",{{"Start Date", type date}, {"End Date", type date}}),
    #"Current Interval" = Table.AddColumn(#"Changed Type", "Interval", each List.Dates([Start Date],Duration.Days([End Date]-[Start Date])+1,#duration(1,0,0,0))),
    #"All Store Bills" = Table.AddColumn(#"Current Interval", "Store Bills", each Table.SelectRows(#"Current Interval",(k)=>k[Store code]=[Store code])),
    #"Min Date" = Table.AddColumn(#"All Store Bills", "Min Date", each List.Min([Store Bills][Start Date])),
    #"Max Date" = Table.AddColumn(#"Min Date", "Max Date", each List.Max([Store Bills][End Date])),
    #"Grouped Rows" = Table.Group(#"Max Date", {"Store code", "Min Date","Max Date"}, {"Combined", each List.Combine([Interval])}),
    #"Full Period" = Table.AddColumn(#"Grouped Rows", "Full Calendar", each List.Dates([Min Date],Duration.Days([Max Date]-[Min Date])+1,#duration(1,0,0,0))),
    Gaps = Table.AddColumn(#"Full Period", "Difference", each List.Difference([Full Calendar],[Combined])),
    #"Removed Other Columns" = Table.SelectColumns(Gaps,{"Store code", "Difference"}),
    #"Expanded Difference" = Table.ExpandListColumn(#"Removed Other Columns", "Difference")
in
    #"Expanded Difference"