Stacking broken using area chart with null values and connectNull: true

I have a chart over last year by month. But have null values for data for first few months.
I have implemented stacking/unstacking via a button. When displaying the stacked chart the data points float above the line where the line should be, but the lines are where the unstacked values would be. If we change connectNull from true to false it works.


{"line":{"connectNull":true},"data":{"type":"area","columns":[["__xs_accounts_low",1483228800000,1485907200000,1488326400000,1491004800000,1493596800000,1496275200000,1498867200000],["__xs_accounts_mid",1483228800000,1485907200000,1488326400000,1491004800000,1493596800000,1496275200000,1498867200000],["__xs_accounts_high",1483228800000,1485907200000,1488326400000,1491004800000,1493596800000,1496275200000,1498867200000],["Accounts: high",null,null,null,21,20,17,13],["Accounts: mid",null,null,null,2,1,5,9],["Accounts: low",null,null,null,4,6,5,5]],"xs":{"Accounts: low":"__xs_accounts_low","Accounts: mid":"__xs_accounts_mid","Accounts: high":"__xs_accounts_high"},"groups":[["Accounts: high","Accounts: mid","Accounts: low"]],"colors":{"Accounts: high":"#7adbb8","Accounts: mid":"#e4c87c","Accounts: low":"#dc8181"},"names":{"Accounts: high":"High","Accounts: mid":"Mid","Accounts: low":"Low"}},"grid":{"y":{"show":true}},"axis":{"x":{"type":"timeseries","tick":{"format":"%b %Y"},"max":1498867200000,"min":1483228800000,"localtime":false,"label":{"text":"Date (UTC)","position":"outer-center"}},"y":{"min":0,"padding":{"bottom":0},"label":{"text":"Accounts","position":"outer-middle"}}},"point":{"show":true,"r":3,"focus":{"expand":{"r":4.5}}},"bindto":"#page_2_1_10 div.chartspace"}

No source file, test, or entry point is named; begin by reproducing the supplied area-chart configuration with connectNull set to true and false. Trace the stacking and null-value handling, then add coverage showing that stacked points align with their stacked areas while unstacked behavior remains unchanged.

Written by the indexing model from the issue text.