public void walk(Handler handler) {
        walkSubtree(this.rootValidatable, new ConfigSaveValidationContext(null), handler);
    }
@Test
    public void shouldWalkPipelineConfigsInMergePipelineConfigs() {
        PipelineConfig pipe = mockPipelineConfig();
        MergePipelineConfigs mergePipelines = new MergePipelineConfigs(new BasicPipelineConfigs(pipe));
        new GoConfigGraphWalker(mergePipelines).walk(Validatable::validate);
        verify(pipe, atLeastOnce()).validate(any(ValidationContext.class));
    }