diff --git a/.changeset/fix-empty-row-save.md b/.changeset/fix-empty-row-save.md
new file mode 100644
index 0000000..52eac11
--- /dev/null
+++ b/.changeset/fix-empty-row-save.md
@@ -0,0 +1,5 @@
+---
+"google-spreadsheet": patch
+---
+
+Fix crash when saving a row with all empty values, and ensure empty cells always return `''` instead of `undefined`
diff --git a/src/lib/GoogleSpreadsheetRow.ts b/src/lib/GoogleSpreadsheetRow.ts
index 48fb400..c49de07 100644
--- a/src/lib/GoogleSpreadsheetRow.ts
+++ b/src/lib/GoogleSpreadsheetRow.ts
@@ -13,7 +13,15 @@ export class GoogleSpreadsheetRow<T extends Record<string, any> = Record<string,
     /** raw underlying data for row */
     private _rawData: any[]
   ) {
+    this._padRawData();
+  }
 
+  /** pad _rawData with empty strings so it always matches header length */
+  private _padRawData() {
+    const headerLength = this._worksheet.headerValues.length;
+    while (this._rawData.length < headerLength) {
+      this._rawData.push('');
+    }
   }
 
   private _deleted = false;
@@ -92,7 +100,8 @@ export class GoogleSpreadsheetRow<T extends Record<string, any> = Record<string,
       },
     });
     const data = await response.json<any>();
-    this._rawData = data.updatedData.values[0];
+    this._rawData = data.updatedData.values?.[0] || [];
+    this._padRawData();
   }
 
   /** delete this row */
diff --git a/src/test/cells.test.ts b/src/test/cells.test.ts
index 804cce4..d651e14 100644
--- a/src/test/cells.test.ts
+++ b/src/test/cells.test.ts
@@ -274,6 +274,109 @@ describe('Cell-based operations', () => {
     });
   });
 
+  describe('merge and unmerge operations', () => {
+    beforeEach(async () => {
+      sheet.resetLocalCache(true);
+    });
+
+    it('merges all cells (MERGE_ALL)', async () => {
+      // set up some values first
+      await sheet.loadCells('A2:B3');
+      sheet.getCell(1, 0).value = 'top-left';
+      sheet.getCell(1, 1).value = 'top-right';
+      sheet.getCell(2, 0).value = 'bot-left';
+      sheet.getCell(2, 1).value = 'bot-right';
+      await sheet.saveUpdatedCells();
+
+      await sheet.mergeCells({
+        startRowIndex: 1,
+        endRowIndex: 3,
+        startColumnIndex: 0,
+        endColumnIndex: 2,
+      });
+
+      await sheet.loadCells('A2:B3');
+      expect(sheet.getCell(1, 0).value).toBe('top-left'); // top-left kept
+      expect(sheet.getCell(1, 1).value).toBeNull(); // merged away
+      expect(sheet.getCell(2, 0).value).toBeNull();
+      expect(sheet.getCell(2, 1).value).toBeNull();
+    });
+
+    it('merges cells in column direction (MERGE_COLUMNS)', async () => {
+      await sheet.loadCells('C2:D3');
+      sheet.getCell(1, 2).value = 'C2';
+      sheet.getCell(1, 3).value = 'D2';
+      sheet.getCell(2, 2).value = 'C3';
+      sheet.getCell(2, 3).value = 'D3';
+      await sheet.saveUpdatedCells();
+
+      await sheet.mergeCells({
+        startRowIndex: 1,
+        endRowIndex: 3,
+        startColumnIndex: 2,
+        endColumnIndex: 4,
+      }, 'MERGE_COLUMNS');
+
+      await sheet.loadCells('C2:D3');
+      expect(sheet.getCell(1, 2).value).toBe('C2'); // top of each column kept
+      expect(sheet.getCell(1, 3).value).toBe('D2');
+      expect(sheet.getCell(2, 2).value).toBeNull(); // merged away
+      expect(sheet.getCell(2, 3).value).toBeNull();
+    });
+
+    it('merges cells in row direction (MERGE_ROWS)', async () => {
+      await sheet.loadCells('E2:F3');
+      sheet.getCell(1, 4).value = 'E2';
+      sheet.getCell(1, 5).value = 'F2';
+      sheet.getCell(2, 4).value = 'E3';
+      sheet.getCell(2, 5).value = 'F3';
+      await sheet.saveUpdatedCells();
+
+      await sheet.mergeCells({
+        startRowIndex: 1,
+        endRowIndex: 3,
+        startColumnIndex: 4,
+        endColumnIndex: 6,
+      }, 'MERGE_ROWS');
+
+      await sheet.loadCells('E2:F3');
+      expect(sheet.getCell(1, 4).value).toBe('E2'); // left of each row kept
+      expect(sheet.getCell(1, 5).value).toBeNull(); // merged away
+      expect(sheet.getCell(2, 4).value).toBe('E3');
+      expect(sheet.getCell(2, 5).value).toBeNull();
+    });
+
+    it('can unmerge cells and write to previously merged cells', async () => {
+      await sheet.loadCells('G2:H2');
+      sheet.getCell(1, 6).value = 'G2';
+      sheet.getCell(1, 7).value = 'H2';
+      await sheet.saveUpdatedCells();
+
+      // merge
+      await sheet.mergeCells({
+        startRowIndex: 1,
+        endRowIndex: 2,
+        startColumnIndex: 6,
+        endColumnIndex: 8,
+      });
+      await sheet.loadCells('G2:H2');
+      expect(sheet.getCell(1, 6).value).toBe('G2');
+      expect(sheet.getCell(1, 7).value).toBeNull();
+
+      // unmerge
+      await sheet.unmergeCells({
+        startRowIndex: 1,
+        endRowIndex: 2,
+        startColumnIndex: 6,
+        endColumnIndex: 8,
+      });
+      await sheet.loadCells('G2:H2');
+      sheet.getCell(1, 7).value = 'restored';
+      await sheet.saveUpdatedCells();
+      expect(sheet.getCell(1, 7).value).toBe('restored');
+    });
+  });
+
   describe.todo('cell formatting', () => {
     // TODO: add tests!
     // - set the background color twice, conflicts b/w backgroundColor and backgroundColorStyle
diff --git a/src/test/data-operations.test.ts b/src/test/data-operations.test.ts
index d86b035..ee3a7b6 100644
--- a/src/test/data-operations.test.ts
+++ b/src/test/data-operations.test.ts
@@ -47,10 +47,10 @@ describe('Data operations - rows, columns, and ranges', () => {
       // header row
       expect(rows[0].get('a')).toEqual('a1');
       expect(rows[0].get('b')).toEqual('b1');
-      expect(rows[1].get('a')).toBeUndefined();
-      expect(rows[1].get('b')).toBeUndefined();
-      expect(rows[2].get('a')).toBeUndefined();
-      expect(rows[2].get('b')).toBeUndefined();
+      expect(rows[1].get('a')).toEqual('');
+      expect(rows[1].get('b')).toEqual('');
+      expect(rows[2].get('a')).toEqual('');
+      expect(rows[2].get('b')).toEqual('');
       expect(rows[3].get('a')).toEqual('a2');
       expect(rows[3].get('b')).toEqual('b2');
     });
diff --git a/src/test/rows.test.ts b/src/test/rows.test.ts
index 3369714..81a485b 100644
--- a/src/test/rows.test.ts
+++ b/src/test/rows.test.ts
@@ -215,6 +215,56 @@ describe('Row-based operations', () => {
       expect(row.get('col3')).toEqual('3'); // it evaluates the formula and formats as a string
     });
 
+    it('can save a row with trailing empty values', async () => {
+      rows = await sheet.getRows();
+      row = rows[0];
+      row.set('numbers', 'hello');
+      row.set('letters', '');
+      row.set('col1', '');
+      row.set('col2', '');
+      row.set('col3', '');
+      await row.save();
+      expect(row.get('numbers')).toBe('hello');
+      // trailing empty values should be empty strings, not undefined
+      expect(row.get('letters')).toBe('');
+      expect(row.get('col1')).toBe('');
+      expect(row.get('col2')).toBe('');
+      expect(row.get('col3')).toBe('');
+    });
+
+    it('empty trailing values persist correctly after re-fetching', async () => {
+      rows = await sheet.getRows();
+      row = rows[0];
+      expect(row.get('numbers')).toBe('hello');
+      expect(row.get('letters')).toBe('');
+      expect(row.get('col3')).toBe('');
+    });
+
+    it('can clear all values in a row by saving empty strings', async () => {
+      rows = await sheet.getRows();
+      row = rows[0];
+      const nonEmptyHeaders = HEADERS.filter((h) => h);
+      _.each(nonEmptyHeaders, (header) => row.set(header, ''));
+      await row.save();
+      _.each(nonEmptyHeaders, (header) => {
+        expect(row.get(header)).toBe('');
+      });
+      // toObject should also return empty strings, not undefined
+      const obj = row.toObject();
+      _.each(nonEmptyHeaders, (header) => {
+        expect(obj[header]).toBe('');
+      });
+    });
+
+    it('all-empty row persists correctly after re-fetching', async () => {
+      rows = await sheet.getRows();
+      row = rows[0];
+      const nonEmptyHeaders = HEADERS.filter((h) => h);
+      _.each(nonEmptyHeaders, (header) => {
+        expect(row.get(header)).toBe('');
+      });
+    });
+
     describe('encoding and odd characters', () => {
       _.each(
         {
@@ -234,83 +284,6 @@ describe('Row-based operations', () => {
     });
   });
 
-  // TODO: Move to cells.test.js because mergeCells and unmergeCells are really cell operations
-  // but they were implemented using the existing data we have here in the rows tests
-  // so we'll leave them here for now
-  describe('merge and unmerge operations', () => {
-    beforeAll(async () => {
-      await sheet.loadCells('A1:H2');
-    });
-
-    const range = {
-      startColumnIndex: 0,
-      endColumnIndex: 2,
-    };
-
-    it('merges all cells', async () => {
-      await sheet.mergeCells({
-        startRowIndex: 2,
-        endRowIndex: 4,
-        ...range,
-      });
-      const mergedRows = await sheet.getRows();
-      expect(mergedRows[1].get('numbers')).toBe('2');
-      expect(mergedRows[1].get('letters')).toBe(undefined);
-      expect(mergedRows[2].get('numbers')).toBe(undefined);
-      expect(mergedRows[2].get('letters')).toBe(undefined);
-    });
-
-    it('merges all cells in column direction', async () => {
-      await sheet.mergeCells({
-        startRowIndex: 4,
-        endRowIndex: 6,
-        ...range,
-      }, 'MERGE_COLUMNS');
-      const mergedRows = await sheet.getRows();
-      expect(mergedRows[3].get('numbers')).toBe('4');
-      expect(mergedRows[3].get('letters')).toBe('E');
-      expect(mergedRows[4].get('numbers')).toBe(undefined);
-      expect(mergedRows[4].get('letters')).toBe(undefined);
-    });
-
-    it('merges all cells in row direction', async () => {
-      await sheet.mergeCells({
-        startRowIndex: 6,
-        endRowIndex: 8,
-        ...range,
-      }, 'MERGE_ROWS');
-      const mergedRows = await sheet.getRows();
-      expect(mergedRows[5].get('numbers')).toBe('6');
-      expect(mergedRows[5].get('letters')).toBe(undefined);
-      expect(mergedRows[6].get('numbers')).toBe('7');
-      expect(mergedRows[6].get('letters')).toBe(undefined);
-    });
-
-    it('unmerges cells', async () => {
-      await sheet.mergeCells({
-        startRowIndex: 8,
-        endRowIndex: 9,
-        ...range,
-      });
-      const mergedRows = await sheet.getRows();
-      expect(mergedRows[7].get('numbers')).toBe('8');
-      expect(mergedRows[7].get('letters')).toBe(undefined);
-      mergedRows[7].set('letters', 'Z');
-      await mergedRows[7].save();
-      expect(mergedRows[7].get('numbers')).toBe('8');
-      expect(mergedRows[7].get('letters')).toBe(undefined);
-      await sheet.unmergeCells({
-        startRowIndex: 8,
-        endRowIndex: 9,
-        ...range,
-      });
-      mergedRows[7].set('letters', 'Z');
-      await mergedRows[7].save();
-      expect(mergedRows[7].get('numbers')).toBe('8');
-      expect(mergedRows[7].get('letters')).toBe('Z');
-    });
-  });
-
   describe('header validation and cleanup', () => {
     let rows: GoogleSpreadsheetRow[];
     beforeAll(async () => {