1. Check if data_ is null before compare it;
2. Always allocate an array for data_ even if size is zero.

Merge pull request !4019 from yao_yf/add_layout_in_stra_ckpt

Merge pull request !3977 from nhussain/multi_dim_concat_2

Merge pull request !3860 from xiefangqi/md_new_api_cocodataset

Merge pull request !3983 from huanghui/reduce-min-fission-pass

Merge pull request !3938 from liubuyu/master

Merge pull request !3807 from 徐永飞/master

Merge pull request !3928 from yihuaijie/dev

Merge pull request !3127 from flywind/infer_2

Merge pull request !3821 from ZhangQinghua/master1

Merge pull request !3103 from yihuaijie/dev

Merge pull request !3820 from zhangbuxue/support_dtype_and_shape_as_attr_in_graph_mode

Added Distributed sampler option

Fix style

Merge pull request !3549 from anthonyaje/device_augment_mapop_refactor1

Merge pull request !3739 from laiyongqiang/eliminate_memcpy_bug

Merge pull request !3119 from dengyutao/remove_blockreader

Merge pull request !3574 from hewei/rename_user_data_func

Merge pull request !3620 from 张学同/to_merge

Refactored MapOp to in preparation to support device augment

Minor fix

Merge pull request !3551 from nhussain/fix_cpp_only_build

Merge pull request !3543 from lianliguang/unify-primitive

Merge pull request !3449 from MahdiRahmaniHanzaki/cifar100-c-api