Stop passing None to compile() in TF examples (#29597)

* Fix examples to stop passing None to compile(), rework example invocation for run_text_classification.py

* Add Amy's fix

examples/tensorflow/text-classification/README.md

@@ -75,7 +75,10 @@ python run_text_classification.py \
 --train_file training_data.json \
 --validation_file validation_data.json \
 --output_dir output/ \
---test_file data_to_predict.json
+--test_file data_to_predict.json \
+--do_train \
+--do_eval \
+--do_predict
 ```
 
 ## run_glue.py

examples/tensorflow/text-classification/run_glue.py

@@ -477,7 +477,7 @@ def main():
                 adam_global_clipnorm=training_args.max_grad_norm,
             )
         else:
-            optimizer = "adam"  # Just write anything because we won't be using it
+            optimizer = "sgd"  # Just write anything because we won't be using it
         if is_regression:
             metrics = []
         else:

examples/tensorflow/text-classification/run_text_classification.py

@@ -526,7 +526,7 @@ def main():
                 adam_global_clipnorm=training_args.max_grad_norm,
             )
         else:
-            optimizer = None
+            optimizer = "sgd"  # Just use any default
         if is_regression:
             metrics = []
         else: