Revert "Remove getNullCell"

This reverts commit 0b6a5b7.

addons/xterm-addon-serialize/src/SerializeAddon.ts

@@ -16,7 +16,9 @@ abstract class BaseSerializeHandler {
   constructor(private _buffer: IBuffer) { }
 
   serialize(startRow: number, endRow: number): string {
-    const { cell1, cell2 } = this._getWorkCells();
+    // we need two of them to flip between old and new cell
+    const cell1 = this._buffer.getNullCell();
+    const cell2 = this._buffer.getNullCell();
     let oldCell = cell1;
 
     this._beforeSerialize(endRow - startRow);
@@ -42,22 +44,6 @@ abstract class BaseSerializeHandler {
     return this._serializeString();
   }
 
-  private _getWorkCells(): { cell1: IBufferCell, cell2: IBufferCell } {
-    const line = this._buffer.getLine(0);
-    if (!line) {
-      throw new Error('Could not fetch first line for serialization');
-    }
-    const cell1 = line.getCell(0);
-    if (!cell1) {
-      throw new Error('Could not fetch first cell for serialization');
-    }
-    const cell2 = line.getCell(0);
-    if (!cell2) {
-      throw new Error('Could not fetch first cell for serialization');
-    }
-    return { cell1, cell2 };
-  }
-
   protected _nextCell(cell: IBufferCell, oldCell: IBufferCell, row: number, col: number): void { }
   protected _rowEnd(row: number): void { }
   protected _beforeSerialize(rows: number): void { }

src/public/Terminal.ts

@@ -204,6 +204,7 @@ class BufferApiView implements IBufferApi {
     }
     return new BufferLineApiView(line);
   }
+  public getNullCell(): IBufferCellApi { return new CellData(); }
 }
 
 class BufferLineApiView implements IBufferLineApi {

typings/xterm.d.ts

@@ -1117,6 +1117,13 @@ declare module 'xterm' {
      * @param y The line index to get.
      */
     getLine(y: number): IBufferLine | undefined;
+
+    /**
+     * Creates an empty cell object suitable as a cell reference in
+     * `line.getCell(x, cell)`. Use this to avoid costly recreation of
+     * cell objects when dealing with tons of cells.
+     */
+    getNullCell(): IBufferCell;
   }
 
   /**