magento-dashboard-graph-api.patch

40c40,41
<     const API_URL = 'http://chart.apis.google.com/chart';
---
>     //const API_URL = 'http://chart.apis.google.com/chart';
>     const API_URL = 'https://image-charts.com/chart'; // use image-charts.com free, since Google's charts API is deprecated and being shut off in first half of March 2019
103c104
<     protected $_encoding = 'e';
---
>     protected $_encoding = 'a';       //
273a275,279
>       } else if ($this->_encoding == "a") {
>           $params['chd'] = "a:";
>             $dataDelimiter = ",";
>             $dataSetdelimiter = ",";
>             $dataMissing = "0";
337a344,354
>           } else if ($this->_encoding == "a") {
>               //array_push($chartdata, implode(",",$thisdataarray[0]));
>               Mage::log("thisdatarray:", 0, "chart.log");
>               Mage::log(var_export($thisdataarray,true),0,"chart.log");
>               foreach ($thisdataarray as $v) {
>                       if (empty($v) || $v==0)
>                               $chartdata[] = $dataMissing;
>                       else
>                               $chartdata[] = $v;
>                       $chartdata[] = $dataDelimiter;
>               }
362a380,382
>       Mage::log("allseries:" . var_export($this->getAllSeries(),true), 0, "chart.log");
>       Mage::log("buffer: " .var_export($buffer,true), 0, "chart.log");
>
438a459,469
>       Mage::log("------", 0, "chart.log");
>       Mage::log("chxl: " . var_export(explode("|",$params['chxl']),true), 0, "chart.log");
>         Mage::log("chxt: " . var_export(explode("|",$params['chxt']),true), 0, "chart.log");
>       Mage::log("chg: " . $params['chg'], 0, "chart.log");
>       Mage::log("chs: " .  $this->getWidth().'x'.$this->getHeight(), 0, "chart.log");
>       Mage::log("------", 0, "chart.log");
>
>
>       Mage::log("params:\n".var_export($params,true), 0, "chart.log");
>

Instructions:
Copy app/code/core/Mage/Adminhtml/Dashboard/Graph.php to app/code/local/Mage/Adminhtml/Dashboard/Graph.php and then apply this patch to it.

See also https://gist.github.com/doctea/34947c7b09b378f6a595effdaa98054b for a script for testing/comparing graph output.