fix nlp import

Author: Divyashree Sreepathihalli

keras_cv/models/feature_extractor/clip/clip_processor.py

@@ -11,8 +11,11 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from keras_nlp.layers import StartEndPacker
 
+try:
+    from keras_nlp.layers import StartEndPacker
+except ImportError:
+    keras_nlp = None
 from keras_cv.api_export import keras_cv_export
 from keras_cv.backend import keras
 from keras_cv.backend import ops
@@ -45,6 +48,11 @@ class CLIPProcessor:
     """
 
     def __init__(self, input_resolution, vocabulary, merges, **kwargs):
+        if keras_nlp is None:
+            raise ValueError(
+                "ClipTokenizer requires keras-nlp. Please install "
+                "using pip `pip install -U keras-nlp && pip install -U keras`"
+            )
         self.input_resolution = input_resolution
         self.vocabulary = vocabulary
         self.merges = merges