src/vs/workbench/common/editor/textEditorModel.ts/BaseTextEditorModel/handleExistingModel
class BaseTextEditorModel:	private handleExistingModel(textEditorModelHandle: URI): void {

		// We need the resource to point to an existing model
		const model = this.modelService.getModel(textEditorModelHandle);
		if (!model) {
			throw new Error(`Document with resource ${textEditorModelHandle.toString(true)} does not exist`);
		}

		this.textEditorModelHandle = textEditorModelHandle;

		// Make sure we clean up when this model gets disposed
		this.registerModelDisposeListener(model);
	}