fix: histogram cannot be rendered properly when data only has step 0 (#807)

frontend/packages/core/builder/mock.js

 /* eslint-disable @typescript-eslint/no-var-requires */
 
 const {middleware} = require('@visualdl/mock');
+const {createProxyMiddleware} = require('http-proxy-middleware');
 
 module.exports = {
-    middleware,
+    middleware: process.env.MOCK
+        ? () => createProxyMiddleware({target: process.env.MOCK, changeOrigin: true})
+        : middleware,
     pathname: '/api'
 };

frontend/packages/core/package.json

@@ -96,6 +96,7 @@
         "enhanced-resolve": "4.3.0",
         "express": "4.17.1",
         "fs-extra": "9.0.1",
+        "http-proxy-middleware": "1.0.5",
         "jest": "26.4.2",
         "snowpack": "2.10.1",
         "typescript": "4.0.2",

frontend/packages/core/src/components/StackChart.tsx

@@ -64,7 +64,7 @@ const StackChart = React.forwardRef<StackChartRef, StackChartProps & WithStyled>
         };
         const rawData = useMemo(() => seriesData.data ?? [], [seriesData.data]);
 
-        const negativeY = useMemo(() => minY - (maxY - minY) * 0.4, [minY, maxY]);
+        const negativeY = useMemo(() => (minY === 0 && maxY === 0 ? -0.4 : minY - (maxY - minY) * 0.4), [minY, maxY]);
 
         const getPoint = useCallback(
             (x: number, y: number, z: number, getCoord: GetCoord) => {