后台的空字符串和null值转为'空'

src/models/parseChartOption.js

@@ -107,7 +107,7 @@ function barOption(data, barConfig, themeConfig, styleConfig, drillDown) {
             },
             data: data.xAxis.map(d => {
                 let gv= xGranularityV;
-                if( !d && d === null ) {
+                if( !d ) {
                     return '空';
                 }
                 let xv = d;