fix: handle trimming null/undefined header values

Author: Theo Ephraim

src/lib/GoogleSpreadsheetWorksheet.ts

@@ -345,7 +345,7 @@ export class GoogleSpreadsheetWorksheet {
  if (!rows) {
  throw new Error('No values in the header row - fill the first row with header values before trying to interact with rows');
  }
- this._headerValues = _.map(rows[0], (header) => header.trim());
+ this._headerValues = _.map(rows[0], (header) => header?.trim());
  if (!_.compact(this.headerValues).length) {
  throw new Error('All your header cells are blank - fill the first row with header values before trying to interact with rows');
  }
@@ -357,7 +357,7 @@ export class GoogleSpreadsheetWorksheet {
  if (headerValues.length > this.columnCount) {
  throw new Error(`Sheet is not large enough to fit ${headerValues.length} columns. Resize the sheet first.`);
  }
- const trimmedHeaderValues = _.map(headerValues, (h) => h.trim());
+ const trimmedHeaderValues = _.map(headerValues, (h) => h?.trim());
  checkForDuplicateHeaders(trimmedHeaderValues);
 
  if (!_.compact(trimmedHeaderValues).length) {