在前端解決顯示null值一例

用.net core2.1 api返回的JSON里包含null值，前端直接顯示出來了，影響閱讀，

用以下語句將null轉換為空字符串：

                        // Build html.
                        html += "<tr>";
                        // Translate Null value to Empty string.
                        for (var key in eBoardJson[i]) {
                            if (eBoardJson[i][key] === null)
                                eBoardJson[i][key] = "";
                            if (key == "matrial")
                                html += "<td style='font-size:14px'>" + eBoardJson[i][key] + "</td>";
                            else
                                html += "<td>" + eBoardJson[i][key] + "</td>";
                        }
                        html += "</tr>";