Init _backbone, _tokenizer and _preprocessor in Task (keras-team#899)

* Init _backbone in Task

* Fix `preprocessor` as well

* format

* Fix `_tokenizer`

* Chain to super() first

Author: jbischof

keras_nlp/models/preprocessor.py

@@ -22,6 +22,10 @@
 class Preprocessor(keras.layers.Layer):
     """Base class for model preprocessors."""
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._tokenizer = None
+
     @property
     def tokenizer(self):
         """The tokenizer used to tokenize strings."""

keras_nlp/models/task.py

@@ -29,6 +29,11 @@
 class Task(PipelineModel):
     """Base class for Task models."""
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self._backbone = None
+        self._preprocessor = None
+
     def preprocess_samples(self, x, y=None, sample_weight=None):
         return self.preprocessor(x, y=y, sample_weight=sample_weight)