Handle missing optional configuration fields correctly (#24)

Co-authored-by: Shaden Smith <ShadenTSmith@gmail.com>
Co-authored-by: Jeff Rasley <jerasley@microsoft.com>

deepspeed/pt/deepspeed_config.py

@@ -256,7 +256,8 @@ class DeepSpeedConfig(object):
         self.dynamic_loss_scale_args = get_dynamic_loss_scale_args(param_dict)
 
         self.optimizer_name = get_optimizer_name(param_dict)
-        if self.optimizer_name.lower() in DEEPSPEED_OPTIMIZERS:
+        if self.optimizer_name is not None and \
+            self.optimizer_name.lower() in DEEPSPEED_OPTIMIZERS:
             self.optimizer_name = self.optimizer_name.lower()
 
         self.optimizer_params = get_optimizer_params(param_dict)

tests/unit/test_ds_config.py

+import pytest
+import os
+import json
+from deepspeed.pt import deepspeed_config as ds_config
+
+
+def test_only_required_fields(tmpdir):
+    '''Ensure that config containing only the required fields is accepted. '''
+    cfg_json = tmpdir.mkdir('ds_config_unit_test').join('minimal.json')
+
+    with open(cfg_json, 'w') as f:
+        required_fields = {'train_batch_size': 64}
+        json.dump(required_fields, f)
+
+    run_cfg = ds_config.DeepSpeedConfig(cfg_json)
+    assert run_cfg is not None
+    assert run_cfg.train_batch_size == 64
+    assert run_cfg.train_micro_batch_size_per_gpu == 64
+    assert run_cfg.gradient_accumulation_steps == 1