raise exception when arguments to pipeline are incomplete (#12548)

* raise exception when arguments are incomplete

* change exception to runtime error

src/transformers/pipelines/__init__.py

@@ -387,6 +387,18 @@ def pipeline(
         >>> tokenizer = AutoTokenizer.from_pretrained("bert-base-cased")
         >>> pipeline('ner', model=model, tokenizer=tokenizer)
     """
+    if model is None and tokenizer is not None:
+        raise RuntimeError(
+            "Impossible to instantiate a pipeline with tokenizer specified but not the model "
+            "as the provided tokenizer may not be compatible with the default model. "
+            "Please provide a PreTrainedModel class or a path/identifier to a pretrained model when providing tokenizer."
+        )
+    if model is None and feature_extractor is not None:
+        raise RuntimeError(
+            "Impossible to instantiate a pipeline with feature_extractor specified but not the model "
+            "as the provided feature_extractor may not be compatible with the default model. "
+            "Please provide a PreTrainedModel class or a path/identifier to a pretrained model when providing feature_extractor."
+        )
 
     # Retrieve the task
     targeted_task, task_options = check_task(task)