message: Fix bug getting typescript compiler when tsjestconfig is undefined
diff: @@ -8,8 +8,8 @@ import { TsJestConfig } from './types';
  * Allows config to specify alternative compiler.
  * For example, `ntypescript`.
  */
  -export function getTypescriptCompiler(config: TsJestConfig): typeof ts_types {
  - const compilerName = typeof config.compiler === 'string' ? config.compiler : 'typescript';
  +export function getTypescriptCompiler(config: TsJestConfig | undefined): typeof ts_types {
  + const compilerName = config && typeof config.compiler === 'string' ? config.compiler : 'typescript';
  try {
  return require(compilerName);
  } catch (err) {
  