diff --git a/main/coreplugins/io.sarl.lang.core/src/io/sarl/lang/core/Agent.java b/main/coreplugins/io.sarl.lang.core/src/io/sarl/lang/core/Agent.java
index 235aca3e7f..d39389197e 100644
--- a/main/coreplugins/io.sarl.lang.core/src/io/sarl/lang/core/Agent.java
+++ b/main/coreplugins/io.sarl.lang.core/src/io/sarl/lang/core/Agent.java
@@ -57,6 +57,8 @@
 @SarlSpecification(SARLVersion.SPECIFICATION_RELEASE_VERSION_STRING)
 public class Agent extends AgentProtectedAPIObject implements Identifiable {
 
+	private static final DynamicSkillProvider SINGLETON = (it0, it1) -> null;
+
 	private final UUID id;
 
 	private final UUID parentID;
@@ -125,7 +127,11 @@ public Agent(
 			DynamicSkillProvider skillProvider) {
 		this.parentID = parentID;
 		this.id = (agentID == null) ? UUID.randomUUID() : agentID;
-		this.skillProvider = skillProvider;
+		if (skillProvider == null) {
+			this.skillProvider = SINGLETON;
+		} else {
+			this.skillProvider = skillProvider;
+		}
 	}
 
 	@Override
@@ -160,7 +166,11 @@ public UUID getID() {
 	 * @since 0.6
 	 */
 	void $setDynamicSkillProvider(DynamicSkillProvider provider) {
-		this.skillProvider = provider;
+		if (provider == null) {
+			this.skillProvider = SINGLETON;
+		} else {
+			this.skillProvider = provider;
+		}
 	}
 
 	/** Replies the skill repository.
@@ -359,39 +369,67 @@ protected final <S extends Capacity> S getSkill(Class<S> capacity) {
 	@Pure
 	protected AtomicClearableReference<Skill> $getSkill(Class<? extends Capacity> capacity) {
 		AtomicClearableReference<Skill> skill = $getSkillRepository().get(capacity);
+		// Check if the stored skill is still not empty
+		if (skill != null) {
+			final Skill s = skill.get();
+			if (s == null) {
+				skill = null;
+			}
+		}
 		if (skill == null) {
 			// Try to load dynamically the skill
-			final DynamicSkillProvider dsp = this.skillProvider;
-			if (dsp != null) {
-				final ClearableReference<Skill> reference = dsp.installSkill(this, capacity);
-				if (reference != null) {
-					return reference;
-				}
+			skill = createSkillFromProvider(capacity);
+			if (skill == null) {
+				// Use the default skill declaration if present.
+				skill = createDefaultSkill(capacity);
 			}
-			// Use the default skill declaration if present.
-			final DefaultSkill annotation = capacity.getAnnotation(DefaultSkill.class);
-			if (annotation != null) {
+			if (skill == null) {
+				throw new UnimplementedCapacityException(capacity, getID());
+			}
+		}
+		return skill;
+	}
+
+	private AtomicClearableReference<Skill> createSkillFromProvider(Class<? extends Capacity> capacity) {
+		assert this.skillProvider != null;
+		final AtomicClearableReference<Skill> reference = this.skillProvider.installSkill(this, capacity);
+		if (reference != null) {
+			final Skill s = reference.get();
+			if (s != null) {
+				return reference;
+			}
+		}
+		return null;
+	}
+
+	private AtomicClearableReference<Skill> createDefaultSkill(Class<? extends Capacity> capacity) {
+		final DefaultSkill annotation = capacity.getAnnotation(DefaultSkill.class);
+		if (annotation != null) {
+			try {
+				final Class<? extends Skill> type = annotation.value();
+				Constructor<? extends Skill> cons;
 				try {
-					final Class<? extends Skill> type = annotation.value();
-					Constructor<? extends Skill> cons;
-					try {
-						cons = type.getConstructor(Agent.class);
-						cons.setAccessible(true);
-						final Skill skillInstance = cons.newInstance(this);
-						return $setSkill(skillInstance);
-					} catch (Throwable exception) {
-						cons = type.getConstructor();
-					}
+					cons = type.getConstructor(Agent.class);
 					cons.setAccessible(true);
-					final Skill skillInstance = cons.newInstance();
+					final Skill skillInstance = cons.newInstance(this);
 					return $setSkill(skillInstance);
 				} catch (Throwable exception) {
-					throw new UnimplementedCapacityException(capacity, getID(), exception);
+					cons = type.getConstructor();
+				}
+				cons.setAccessible(true);
+				final Skill skillInstance = cons.newInstance();
+				final AtomicClearableReference<Skill> ref = $setSkill(skillInstance);
+				if (ref != null) {
+					final Skill s = ref.get();
+					if (s != null) {
+						return ref;
+					}
 				}
+			} catch (Throwable exception) {
+				throw new UnimplementedCapacityException(capacity, getID(), exception);
 			}
-			throw new UnimplementedCapacityException(capacity, getID());
 		}
-		return skill;
+		return null;
 	}
 
 	@Override
diff --git a/tests/io.sarl.lang.core.tests/src/test/java/io/sarl/lang/core/tests/core/AgentTest.java b/tests/io.sarl.lang.core.tests/src/test/java/io/sarl/lang/core/tests/core/AgentTest.java
index 2e4197cd39..0d146d99b5 100644
--- a/tests/io.sarl.lang.core.tests/src/test/java/io/sarl/lang/core/tests/core/AgentTest.java
+++ b/tests/io.sarl.lang.core.tests/src/test/java/io/sarl/lang/core/tests/core/AgentTest.java
@@ -47,6 +47,7 @@
 import io.sarl.lang.core.Capacity;
 import io.sarl.lang.core.DefaultSkill;
 import io.sarl.lang.core.Event;
+import io.sarl.lang.core.SREutils;
 import io.sarl.lang.core.Skill;
 import io.sarl.lang.core.UnimplementedCapacityException;
 import io.sarl.lang.util.AtomicClearableReference;
@@ -451,6 +452,94 @@ public void getSkill_defaultskill() throws Exception {
 		assertSame(ref0, ref1);
 	}
 
+	@Test
+	public void getSkill_noRegistration() throws Exception {
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity4.class);
+		});
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity5.class);
+		});
+	}
+
+	@Test
+	public void getSkill_registrationSkill6() throws Exception {
+		Skill expected = new Skill6();
+		SREutils.setInternalSkill(this.agent, expected, new Class[0]);
+		//
+		AtomicClearableReference<Skill> actual = this.agent.$getSkill(Capacity4.class);
+		assertNotNull(actual);
+		assertSame(expected, actual.get());
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity5.class);
+		});
+	}
+
+	@Test
+	public void getSkill_registrationSkill7() throws Exception {
+		Skill expected = new Skill7();
+		SREutils.setInternalSkill(this.agent, expected, new Class[0]);
+		//
+		AtomicClearableReference<Skill> actual0 = this.agent.$getSkill(Capacity4.class);
+		assertNotNull(actual0);
+		assertSame(expected, actual0.get());
+		//
+		AtomicClearableReference<Skill> actual1 = this.agent.$getSkill(Capacity5.class);
+		assertNotNull(actual1);
+		assertSame(expected, actual1.get());
+	}
+
+	@Test
+	public void getSkill_registrationSkill6_clearReference() throws Exception {
+		Skill expected = new Skill6();
+		SREutils.setInternalSkill(this.agent, expected, new Class[0]).clear();
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity4.class);
+		});
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity5.class);
+		});
+	}
+
+	@Test
+	public void getSkill_registrationSkill7_clearReference0() throws Exception {
+		Skill expected = new Skill7();
+		// The following line clear the Capacity5 reference only.
+		SREutils.setInternalSkill(this.agent, expected, new Class[0]).clear();
+		//
+		AtomicClearableReference<Skill> actual = this.agent.$getSkill(Capacity4.class);
+		assertNotNull(actual);
+		assertSame(expected, actual.get());
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity5.class);
+		});
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity5.class);
+		});
+	}
+
+	@Test
+	public void getSkill_registrationSkill7_clearReference1() throws Exception {
+		Skill expected = new Skill7();
+		// The following line clear the Capacity5 reference only.
+		SREutils.setInternalSkill(this.agent, expected, new Class[0]).clear();
+		// The following line clear the Capacity4 reference only.
+		SREutils.getInternalSkillReference(this.agent, Capacity4.class).clear();
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity4.class);
+		});
+		//
+		assertException(UnimplementedCapacityException.class, () -> {
+			this.agent.$getSkill(Capacity5.class);
+		});
+	}
+
 	/** Only for making public several protected methods.
 	 *
 	 * @author $Author: sgalland$
@@ -470,7 +559,6 @@ public AgentMock(UUID parentID) {
 		public <S extends Skill> S setSkill_Fake(S skill, Class<? extends Capacity>... capacity) {
 			return setSkill(skill, capacity);
 		}
-
 		
 		@Override
 		public AtomicClearableReference<Skill> $getSkill(Class<? extends Capacity> capacity) {
@@ -577,6 +665,50 @@ public Skill3() {
 		}
 	}
 
+	/**
+	 * @author $Author: sgalland$
+	 * @version $FullVersion$
+	 * @mavengroupid $GroupId$
+	 * @mavenartifactid $ArtifactId$
+	 */
+	private static interface Capacity4 extends Capacity {
+		//
+	}
+
+	/**
+	 * @author $Author: sgalland$
+	 * @version $FullVersion$
+	 * @mavengroupid $GroupId$
+	 * @mavenartifactid $ArtifactId$
+	 */
+	private static interface Capacity5 extends Capacity4 {
+		//
+	}
+
+	/**
+	 * @author $Author: sgalland$
+	 * @version $FullVersion$
+	 * @mavengroupid $GroupId$
+	 * @mavenartifactid $ArtifactId$
+	 */
+	private static class Skill6 extends Skill implements Capacity4 {
+		public Skill6() {
+			//
+		}
+	}
+
+	/**
+	 * @author $Author: sgalland$
+	 * @version $FullVersion$
+	 * @mavengroupid $GroupId$
+	 * @mavenartifactid $ArtifactId$
+	 */
+	private static class Skill7 extends Skill implements Capacity5 {
+		public Skill7() {
+			//
+		}
+	}
+
 	/**
 	 * @author $Author: sgalland$
 	 * @version $FullVersion$