Fix: Missing a MetadataConfigs init when the repo has a `datasets_info.json` but no README

When I try to push to an arrow repo (can provide the link on Slack), it uploads the files but fails to update the metadata, with
```
  File "app.py", line 123, in add_new_eval
    eval_results[level].push_to_hub(my_repo, token=TOKEN, split=SPLIT)
  File "blabla_my_env_path/lib/python3.10/site-packages/datasets/arrow_dataset.py", line 5501, in push_to_hub
    if not metadata_configs:
UnboundLocalError: local variable 'metadata_configs' referenced before assignment
```

This fixes it.

Comments:
_The documentation is not available anymore as the PR was closed or merged._

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.006874 / 0.011353 (-0.004479) | 0.004276 / 0.011008 (-0.006732) | 0.085198 / 0.038508 (0.046690) | 0.084281 / 0.023109 (0.061171) | 0.344767 / 0.275898 (0.068869) | 0.377798 / 0.323480 (0.054318) | 0.005656 / 0.007986 (-0.002330) | 0.003601 / 0.004328 (-0.000727) | 0.065486 / 0.004250 (0.061235) | 0.056191 / 0.037052 (0.019139) | 0.351412 / 0.258489 (0.092923) | 0.398591 / 0.293841 (0.104750) | 0.031662 / 0.128546 (-0.096884) | 0.008901 / 0.075646 (-0.066745) | 0.290423 / 0.419271 (-0.128849) | 0.053793 / 0.043533 (0.010260) | 0.347968 / 0.255139 (0.092829) | 0.376978 / 0.283200 (0.093778) | 0.026745 / 0.141683 (-0.114938) | 1.514119 / 1.452155 (0.061964) | 1.580920 / 1.492716 (0.088203) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.273648 / 0.018006 (0.255642) | 0.575176 / 0.000490 (0.574686) | 0.003557 / 0.000200 (0.003357) | 0.000093 / 0.000054 (0.000038) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.031714 / 0.037411 (-0.005697) | 0.089166 / 0.014526 (0.074640) | 0.101525 / 0.176557 (-0.075032) | 0.161855 / 0.737135 (-0.575281) | 0.101391 / 0.296338 (-0.194947) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.380947 / 0.215209 (0.165738) | 3.800527 / 2.077655 (1.722873) | 1.820789 / 1.504120 (0.316669) | 1.657327 / 1.541195 (0.116132) | 1.776242 / 1.468490 (0.307752) | 0.486954 / 4.584777 (-4.097823) | 3.688340 / 3.745712 (-0.057372) | 3.354453 / 5.269862 (-1.915409) | 2.119995 / 4.565676 (-2.445682) | 0.057446 / 0.424275 (-0.366829) | 0.007752 / 0.007607 (0.000145) | 0.461907 / 0.226044 (0.235862) | 4.617870 / 2.268929 (2.348942) | 2.337025 / 55.444624 (-53.107599) | 1.964770 / 6.876477 (-4.911707) | 2.252066 / 2.142072 (0.109993) | 0.591585 / 4.805227 (-4.213642) | 0.134655 / 6.500664 (-6.366009) | 0.060646 / 0.075469 (-0.014823) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.263271 / 1.841788 (-0.578517) | 20.822286 / 8.074308 (12.747978) | 14.710256 / 10.191392 (4.518864) | 0.167285 / 0.680424 (-0.513139) | 0.018302 / 0.534201 (-0.515899) | 0.401023 / 0.579283 (-0.178260) | 0.428956 / 0.434364 (-0.005407) | 0.466120 / 0.540337 (-0.074218) | 0.637868 / 1.386936 (-0.749069) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.007174 / 0.011353 (-0.004179) | 0.004418 / 0.011008 (-0.006590) | 0.065731 / 0.038508 (0.027223) | 0.090457 / 0.023109 (0.067348) | 0.387306 / 0.275898 (0.111408) | 0.427178 / 0.323480 (0.103698) | 0.005699 / 0.007986 (-0.002286) | 0.003662 / 0.004328 (-0.000666) | 0.066190 / 0.004250 (0.061940) | 0.062860 / 0.037052 (0.025808) | 0.388855 / 0.258489 (0.130366) | 0.427853 / 0.293841 (0.134012) | 0.032770 / 0.128546 (-0.095776) | 0.008780 / 0.075646 (-0.066866) | 0.071156 / 0.419271 (-0.348116) | 0.050174 / 0.043533 (0.006641) | 0.385254 / 0.255139 (0.130115) | 0.405069 / 0.283200 (0.121869) | 0.025561 / 0.141683 (-0.116122) | 1.506907 / 1.452155 (0.054752) | 1.543270 / 1.492716 (0.050554) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.304651 / 0.018006 (0.286645) | 0.577269 / 0.000490 (0.576780) | 0.004479 / 0.000200 (0.004279) | 0.000127 / 0.000054 (0.000073) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.034070 / 0.037411 (-0.003341) | 0.097664 / 0.014526 (0.083138) | 0.106969 / 0.176557 (-0.069588) | 0.163093 / 0.737135 (-0.574043) | 0.109384 / 0.296338 (-0.186955) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.414823 / 0.215209 (0.199614) | 4.148390 / 2.077655 (2.070735) | 2.114038 / 1.504120 (0.609918) | 1.959316 / 1.541195 (0.418121) | 2.098138 / 1.468490 (0.629648) | 0.486338 / 4.584777 (-4.098439) | 3.642850 / 3.745712 (-0.102863) | 3.458311 / 5.269862 (-1.811551) | 2.185662 / 4.565676 (-2.380014) | 0.057555 / 0.424275 (-0.366720) | 0.007522 / 0.007607 (-0.000085) | 0.497975 / 0.226044 (0.271931) | 4.971528 / 2.268929 (2.702600) | 2.614087 / 55.444624 (-52.830537) | 2.288406 / 6.876477 (-4.588070) | 2.564067 / 2.142072 (0.421995) | 0.582248 / 4.805227 (-4.222979) | 0.134931 / 6.500664 (-6.365733) | 0.062689 / 0.075469 (-0.012780) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.343331 / 1.841788 (-0.498457) | 21.398950 / 8.074308 (13.324642) | 14.620971 / 10.191392 (4.429579) | 0.169779 / 0.680424 (-0.510644) | 0.018683 / 0.534201 (-0.515518) | 0.396152 / 0.579283 (-0.183131) | 0.409596 / 0.434364 (-0.024768) | 0.482875 / 0.540337 (-0.057463) | 0.659977 / 1.386936 (-0.726959) |

</details>
</details>

![](https://cml.dev/watermark.png#1fd2234b8c802d47db5a5aa939148f98c9c49350 "CML watermark")


<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.006662 / 0.011353 (-0.004691) | 0.003959 / 0.011008 (-0.007049) | 0.084447 / 0.038508 (0.045939) | 0.070267 / 0.023109 (0.047158) | 0.310301 / 0.275898 (0.034403) | 0.339866 / 0.323480 (0.016386) | 0.004008 / 0.007986 (-0.003977) | 0.003270 / 0.004328 (-0.001058) | 0.064997 / 0.004250 (0.060746) | 0.053151 / 0.037052 (0.016099) | 0.327867 / 0.258489 (0.069378) | 0.368560 / 0.293841 (0.074719) | 0.031436 / 0.128546 (-0.097111) | 0.008547 / 0.075646 (-0.067099) | 0.288513 / 0.419271 (-0.130758) | 0.051833 / 0.043533 (0.008300) | 0.312660 / 0.255139 (0.057521) | 0.347180 / 0.283200 (0.063980) | 0.024982 / 0.141683 (-0.116701) | 1.472487 / 1.452155 (0.020333) | 1.550138 / 1.492716 (0.057422) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.208443 / 0.018006 (0.190437) | 0.451927 / 0.000490 (0.451437) | 0.004452 / 0.000200 (0.004252) | 0.000082 / 0.000054 (0.000027) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.029164 / 0.037411 (-0.008247) | 0.085801 / 0.014526 (0.071275) | 0.096229 / 0.176557 (-0.080327) | 0.153063 / 0.737135 (-0.584072) | 0.097712 / 0.296338 (-0.198626) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.383969 / 0.215209 (0.168760) | 3.829216 / 2.077655 (1.751561) | 1.854466 / 1.504120 (0.350346) | 1.684149 / 1.541195 (0.142954) | 1.759422 / 1.468490 (0.290932) | 0.480229 / 4.584777 (-4.104548) | 3.653363 / 3.745712 (-0.092349) | 3.264456 / 5.269862 (-2.005406) | 2.020579 / 4.565676 (-2.545097) | 0.056920 / 0.424275 (-0.367355) | 0.007625 / 0.007607 (0.000018) | 0.458559 / 0.226044 (0.232515) | 4.580288 / 2.268929 (2.311359) | 2.353783 / 55.444624 (-53.090841) | 1.967223 / 6.876477 (-4.909253) | 2.182707 / 2.142072 (0.040634) | 0.631341 / 4.805227 (-4.173886) | 0.141656 / 6.500664 (-6.359008) | 0.059918 / 0.075469 (-0.015551) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.279635 / 1.841788 (-0.562153) | 19.725763 / 8.074308 (11.651455) | 14.477946 / 10.191392 (4.286554) | 0.164360 / 0.680424 (-0.516064) | 0.018286 / 0.534201 (-0.515915) | 0.394935 / 0.579283 (-0.184348) | 0.419638 / 0.434364 (-0.014726) | 0.460366 / 0.540337 (-0.079972) | 0.636876 / 1.386936 (-0.750060) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.006568 / 0.011353 (-0.004785) | 0.004270 / 0.011008 (-0.006738) | 0.065522 / 0.038508 (0.027014) | 0.071597 / 0.023109 (0.048487) | 0.394929 / 0.275898 (0.119031) | 0.427548 / 0.323480 (0.104068) | 0.005320 / 0.007986 (-0.002665) | 0.003366 / 0.004328 (-0.000962) | 0.065780 / 0.004250 (0.061530) | 0.055390 / 0.037052 (0.018338) | 0.397950 / 0.258489 (0.139461) | 0.435800 / 0.293841 (0.141959) | 0.031816 / 0.128546 (-0.096730) | 0.008555 / 0.075646 (-0.067091) | 0.072110 / 0.419271 (-0.347161) | 0.049077 / 0.043533 (0.005544) | 0.390065 / 0.255139 (0.134926) | 0.410294 / 0.283200 (0.127094) | 0.023389 / 0.141683 (-0.118294) | 1.491491 / 1.452155 (0.039336) | 1.551057 / 1.492716 (0.058341) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.243869 / 0.018006 (0.225862) | 0.451961 / 0.000490 (0.451471) | 0.019834 / 0.000200 (0.019634) | 0.000114 / 0.000054 (0.000059) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.031031 / 0.037411 (-0.006380) | 0.088189 / 0.014526 (0.073663) | 0.101743 / 0.176557 (-0.074814) | 0.155236 / 0.737135 (-0.581899) | 0.101245 / 0.296338 (-0.195094) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.422178 / 0.215209 (0.206969) | 4.199989 / 2.077655 (2.122334) | 2.228816 / 1.504120 (0.724696) | 2.057172 / 1.541195 (0.515978) | 2.162651 / 1.468490 (0.694161) | 0.491186 / 4.584777 (-4.093591) | 3.666221 / 3.745712 (-0.079491) | 3.289531 / 5.269862 (-1.980331) | 2.050027 / 4.565676 (-2.515650) | 0.057464 / 0.424275 (-0.366811) | 0.007379 / 0.007607 (-0.000228) | 0.506532 / 0.226044 (0.280487) | 5.066385 / 2.268929 (2.797456) | 2.694405 / 55.444624 (-52.750219) | 2.372200 / 6.876477 (-4.504277) | 2.562724 / 2.142072 (0.420652) | 0.615474 / 4.805227 (-4.189753) | 0.148284 / 6.500664 (-6.352380) | 0.061380 / 0.075469 (-0.014089) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.332649 / 1.841788 (-0.509139) | 20.591063 / 8.074308 (12.516755) | 14.105253 / 10.191392 (3.913861) | 0.151886 / 0.680424 (-0.528537) | 0.018200 / 0.534201 (-0.516001) | 0.395278 / 0.579283 (-0.184005) | 0.407113 / 0.434364 (-0.027251) | 0.473168 / 0.540337 (-0.067170) | 0.660766 / 1.386936 (-0.726170) |

</details>
</details>

![](https://cml.dev/watermark.png#8b8e6ee067eb74e7965ca2a6768f15f9398cb7c8 "CML watermark")