fix(legend): fix dataItem undefined error

Author: roojay520

src/component/legend/LegendModel.ts

@@ -362,6 +362,13 @@ class LegendModel<Ops extends LegendOption = LegendOption> extends ComponentMode
                     name: dataItem as string
                 };
             }
+
+            const isNil = (val: any) => val === null || val === undefined || val === '';
+            // remove empty legend names
+            if(isNil(dataItem) || isNil(dataItem.name)) {
+                return null;
+            }
+
             if (legendNameMap.get(dataItem.name)) {
                 // remove legend name duplicate
                 return null;