diff --git a/miplearn/components/component.py b/miplearn/components/component.py
index 355d587..c2eea0d 100644
--- a/miplearn/components/component.py
+++ b/miplearn/components/component.py
@@ -132,17 +132,17 @@ class Component:
         return
 
     @staticmethod
-    def xy_sample(
+    def xy(
         features: Features,
         sample: TrainingSample,
-    ) -> Optional[Tuple[Dict, Dict]]:
+    ) -> Tuple[Dict, Dict]:
         """
         Given a set of features and a training sample, returns a pair of x and y
         dictionaries containing, respectively, the matrices of ML features and the
         labels for the sample. If the training sample does not include label
-        information, returns None.
+        information, returns (x, {}).
         """
-        return None
+        pass
 
     def xy_instances(
         self,
@@ -153,7 +153,7 @@ class Component:
         for instance in InstanceIterator(instances):
             assert isinstance(instance, Instance)
             for sample in instance.training_data:
-                xy = self.xy_sample(instance.features, sample)
+                xy = self.xy(instance.features, sample)
                 if xy is None:
                     continue
                 x_sample, y_sample = xy
diff --git a/miplearn/components/lazy_static.py b/miplearn/components/lazy_static.py
index 29432dc..c2006a0 100644
--- a/miplearn/components/lazy_static.py
+++ b/miplearn/components/lazy_static.py
@@ -207,12 +207,10 @@ class StaticLazyConstraintsComponent(Component):
         return result
 
     @staticmethod
-    def xy_sample(
+    def xy(
         features: Features,
         sample: TrainingSample,
-    ) -> Optional[Tuple[Dict, Dict]]:
-        if "LazyStatic: Enforced" not in sample:
-            return None
+    ) -> Tuple[Dict, Dict]:
         x: Dict = {}
         y: Dict = {}
         for (cid, cfeatures) in features["Constraints"].items():
@@ -225,8 +223,9 @@ class StaticLazyConstraintsComponent(Component):
                 x[category] = []
                 y[category] = []
             x[category] += [cfeatures["User features"]]
-            if cid in sample["LazyStatic: Enforced"]:
-                y[category] += [[False, True]]
-            else:
-                y[category] += [[True, False]]
+            if "LazyStatic: Enforced" in sample:
+                if cid in sample["LazyStatic: Enforced"]:
+                    y[category] += [[False, True]]
+                else:
+                    y[category] += [[True, False]]
         return x, y
diff --git a/miplearn/components/objective.py b/miplearn/components/objective.py
index 270a8f3..d928c5a 100644
--- a/miplearn/components/objective.py
+++ b/miplearn/components/objective.py
@@ -166,12 +166,10 @@ class ObjectiveValueComponent(Component):
         return ev
 
     @staticmethod
-    def xy_sample(
+    def xy(
         features: Features,
         sample: TrainingSample,
-    ) -> Optional[Tuple[Dict, Dict]]:
-        if "Lower bound" not in sample:
-            return None
+    ) -> Tuple[Dict, Dict]:
         f = features["Instance"]["User features"]
         if "LP value" in sample and sample["LP value"] is not None:
             f += [sample["LP value"]]
@@ -179,8 +177,11 @@ class ObjectiveValueComponent(Component):
             "Lower bound": [f],
             "Upper bound": [f],
         }
-        y = {
-            "Lower bound": [[sample["Lower bound"]]],
-            "Upper bound": [[sample["Upper bound"]]],
-        }
-        return x, y
+        if "Lower bound" in sample:
+            y = {
+                "Lower bound": [[sample["Lower bound"]]],
+                "Upper bound": [[sample["Upper bound"]]],
+            }
+            return x, y
+        else:
+            return x, {}
diff --git a/miplearn/components/primal.py b/miplearn/components/primal.py
index 797a082..70b93a2 100644
--- a/miplearn/components/primal.py
+++ b/miplearn/components/primal.py
@@ -134,7 +134,7 @@ class PrimalSolutionComponent(Component):
                 solution[var_name][idx] = None
 
         # Compute y_pred
-        x = self.x_sample(features, sample)
+        x, _ = self.xy(features, sample)
         y_pred = {}
         for category in x.keys():
             assert category in self.classifiers, (
@@ -173,7 +173,7 @@ class PrimalSolutionComponent(Component):
         ):
             instance = instances[instance_idx]
             solution_actual = instance.training_data[0]["Solution"]
-            solution_pred = self.predict(instance)
+            solution_pred = self.predict(instance, instance.training_data[0])
 
             vars_all, vars_one, vars_zero = set(), set(), set()
             pred_one_positive, pred_zero_positive = set(), set()
@@ -213,33 +213,10 @@ class PrimalSolutionComponent(Component):
         return ev
 
     @staticmethod
-    def xy_sample(
+    def xy(
         features: Features,
         sample: TrainingSample,
-    ) -> Optional[Tuple[Dict, Dict]]:
-        if "Solution" not in sample:
-            return None
-        assert sample["Solution"] is not None
-        return cast(
-            Tuple[Dict, Dict],
-            PrimalSolutionComponent._extract(features, sample),
-        )
-
-    @staticmethod
-    def x_sample(
-        features: Features,
-        sample: TrainingSample,
-    ) -> Dict:
-        return cast(
-            Dict,
-            PrimalSolutionComponent._extract(features, sample),
-        )
-
-    @staticmethod
-    def _extract(
-        features: Features,
-        sample: TrainingSample,
-    ) -> Union[Dict, Tuple[Dict, Dict]]:
+    ) -> Tuple[Dict, Dict]:
         x: Dict = {}
         y: Dict = {}
         solution: Optional[Solution] = None
@@ -271,7 +248,4 @@ class PrimalSolutionComponent(Component):
                         "category to None."
                     )
                     y[category] += [[opt_value < 0.5, opt_value >= 0.5]]
-        if solution is not None:
-            return x, y
-        else:
-            return x
+        return x, y
diff --git a/tests/components/test_component.py b/tests/components/test_component.py
index e03257a..3688aa9 100644
--- a/tests/components/test_component.py
+++ b/tests/components/test_component.py
@@ -57,7 +57,7 @@ def test_xy_instance():
     instance_2 = Mock(spec=Instance)
     instance_2.training_data = ["s3"]
     instance_2.features = {}
-    comp.xy_sample = _xy_sample
+    comp.xy = _xy_sample
     x_expected = {
         "category_a": [
             [1, 2, 3],
diff --git a/tests/components/test_lazy_static.py b/tests/components/test_lazy_static.py
index 8cd7991..b1001d1 100644
--- a/tests/components/test_lazy_static.py
+++ b/tests/components/test_lazy_static.py
@@ -286,7 +286,7 @@ def test_xy_sample() -> None:
             [False, True],
         ],
     }
-    xy = StaticLazyConstraintsComponent.xy_sample(features, sample)
+    xy = StaticLazyConstraintsComponent.xy(features, sample)
     assert xy is not None
     x_actual, y_actual = xy
     assert x_actual == x_expected
diff --git a/tests/components/test_objective.py b/tests/components/test_objective.py
index f9d7dcc..bbd93cd 100644
--- a/tests/components/test_objective.py
+++ b/tests/components/test_objective.py
@@ -125,7 +125,7 @@ def test_xy_sample_with_lp() -> None:
         "Lower bound": [[1.0]],
         "Upper bound": [[2.0]],
     }
-    xy = ObjectiveValueComponent.xy_sample(features, sample)
+    xy = ObjectiveValueComponent.xy(features, sample)
     assert xy is not None
     x_actual, y_actual = xy
     assert x_actual == x_expected
@@ -150,7 +150,7 @@ def test_xy_sample_without_lp() -> None:
         "Lower bound": [[1.0]],
         "Upper bound": [[2.0]],
     }
-    xy = ObjectiveValueComponent.xy_sample(features, sample)
+    xy = ObjectiveValueComponent.xy(features, sample)
     assert xy is not None
     x_actual, y_actual = xy
     assert x_actual == x_expected
diff --git a/tests/components/test_primal.py b/tests/components/test_primal.py
index 6785843..4f7b620 100644
--- a/tests/components/test_primal.py
+++ b/tests/components/test_primal.py
@@ -8,15 +8,14 @@ import numpy as np
 from numpy.testing import assert_array_equal
 from scipy.stats import randint
 
-from miplearn import Classifier, LearningSolver, GurobiSolver, GurobiPyomoSolver
+from miplearn import Classifier, LearningSolver
 from miplearn.classifiers.threshold import Threshold
 from miplearn.components.primal import PrimalSolutionComponent
 from miplearn.problems.tsp import TravelingSalesmanGenerator
 from miplearn.types import TrainingSample, Features
-from tests.fixtures.knapsack import get_knapsack_instance
 
 
-def test_xy_sample_with_lp_solution() -> None:
+def test_xy() -> None:
     features: Features = {
         "Variables": {
             "x": {
@@ -70,14 +69,14 @@ def test_xy_sample_with_lp_solution() -> None:
             [True, False],
         ]
     }
-    xy = PrimalSolutionComponent.xy_sample(features, sample)
+    xy = PrimalSolutionComponent.xy(features, sample)
     assert xy is not None
     x_actual, y_actual = xy
     assert x_actual == x_expected
     assert y_actual == y_expected
 
 
-def test_xy_sample_without_lp_solution() -> None:
+def test_xy_without_lp_solution() -> None:
     features: Features = {
         "Variables": {
             "x": {
@@ -123,7 +122,7 @@ def test_xy_sample_without_lp_solution() -> None:
             [True, False],
         ]
     }
-    xy = PrimalSolutionComponent.xy_sample(features, sample)
+    xy = PrimalSolutionComponent.xy(features, sample)
     assert xy is not None
     x_actual, y_actual = xy
     assert x_actual == x_expected
@@ -170,7 +169,7 @@ def test_predict() -> None:
             }
         }
     }
-    x = PrimalSolutionComponent.x_sample(features, sample)
+    x, _ = PrimalSolutionComponent.xy(features, sample)
     comp = PrimalSolutionComponent()
     comp.classifiers = {"default": clf}
     comp.thresholds = {"default": thr}