code: private static Method lambdaMethod( SerializedLambda serialized )
      {
          Class<?> implClass = lambdaClass( serialized );
          return Stream.of( implClass.getDeclaredMethods() )
                       .filter( method -> Objects.equals( method.getName(), serialized.getImplMethodName() ) )
                       .reduce( ( l, r ) -> {
                           throw new IllegalArgumentException( "Too many implementation methods." );
                       } )
                       .orElseThrow( () -> new IllegalStateException( "Unable to find implementation method." ) );
      }
docs: Get the implementation method of a ({@linkplain Serializable serializable}) lambda.
  
  @param serialized the serialized form of a lambda.
  @return the {@link Method} that implements the lambda.