diff --git a/easy-rules-core/pom.xml b/easy-rules-core/pom.xml
index 7943783..fab3ef9 100644
--- a/easy-rules-core/pom.xml
+++ b/easy-rules-core/pom.xml
@@ -92,6 +92,12 @@
       <artifactId>jsr305</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.jspecify</groupId>
+      <artifactId>jspecify</artifactId>
+      <version>1.0.0</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>
diff --git a/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleProxy.java b/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleProxy.java
index 0819531..9bcba58 100644
--- a/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleProxy.java
+++ b/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleProxy.java
@@ -29,6 +29,7 @@
 import java.lang.reflect.InvocationHandler;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.lang.reflect.Parameter;
 import java.lang.reflect.Proxy;
 import java.util.ArrayList;
 import java.util.Iterator;
@@ -175,8 +176,8 @@ private Object compareToMethod(final Object[] args) throws Exception {
 
   private List<Object> getActualParameters(Method method, Facts facts) {
     List<Object> actualParameters = new ArrayList<>();
-    Annotation[][] parameterAnnotations = method.getParameterAnnotations();
-    for (Annotation[] annotations : parameterAnnotations) {
+    for (Parameter parameter : method.getParameters()) {
+      Annotation[] annotations = parameter.getAnnotations();
       String factName = null;
       boolean annotatedAsNullable = false;
       for (Annotation annotation : annotations) {
@@ -186,6 +187,11 @@ private List<Object> getActualParameters(Method method, Facts facts) {
           annotatedAsNullable = true;
         }
       }
+      for (Annotation annotation : parameter.getAnnotatedType().getAnnotations()) {
+        if (RulesEngineParameters.hasOptionalParameterAnnotation(annotation.annotationType())) {
+          annotatedAsNullable = true;
+        }
+      }
       if (factName != null) {
         Object fact = facts.get(factName); //validated upfront.
         if (fact == null && !facts.asMap().containsKey(factName) && !annotatedAsNullable) {
diff --git a/easy-rules-core/src/test/java/org/jeasy/rules/core/OptionalFactTypeAnnotationParameterTest.java b/easy-rules-core/src/test/java/org/jeasy/rules/core/OptionalFactTypeAnnotationParameterTest.java
new file mode 100644
index 0000000..15d5f3f
--- /dev/null
+++ b/easy-rules-core/src/test/java/org/jeasy/rules/core/OptionalFactTypeAnnotationParameterTest.java
@@ -0,0 +1,127 @@
+/*
+ * The MIT License
+ *
+ *  Copyright (c) 2022, Mahmoud Ben Hassine (mahmoud.benhassine@icloud.com)
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining a copy
+ *  of this software and associated documentation files (the "Software"), to deal
+ *  in the Software without restriction, including without limitation the rights
+ *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *  copies of the Software, and to permit persons to whom the Software is
+ *  furnished to do so, subject to the following conditions:
+ *
+ *  The above copyright notice and this permission notice shall be included in
+ *  all copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ *  THE SOFTWARE.
+ */
+package org.jeasy.rules.core;
+
+import org.jeasy.rules.annotation.Action;
+import org.jeasy.rules.annotation.Condition;
+import org.jeasy.rules.annotation.Fact;
+import org.jeasy.rules.annotation.Rule;
+import org.jeasy.rules.api.Facts;
+import org.jeasy.rules.api.Rules;
+import org.jeasy.rules.api.RulesEngineParameters;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.jspecify.annotations.Nullable;
+import java.util.Map;
+
+/** Null facts are not accepted by design, a declared fact can be missing though. */
+public class OptionalFactTypeAnnotationParameterTest extends AbstractTest {
+
+  @BeforeEach
+  public void setup() throws Exception {
+    facts = new Facts();
+    facts.put("fact1", fact1);
+    facts.put("fact2", fact2);
+    rules = new Rules();
+
+    RulesEngineParameters rulesEngineParameters = new RulesEngineParameters();
+    rulesEngineParameters.setFailsOnException(true);
+    rulesEngine = new DefaultRulesEngine(rulesEngineParameters);
+  }
+
+  @AfterEach
+  void cleanup() {
+    RulesEngineParameters.setOptionalParameterAnnotation(null);
+  }
+
+  @Test
+  public void testMissingFact() {
+    RulesEngineParameters.setOptionalParameterAnnotation(Nullable.class);
+    Rules rules = new Rules();
+    rules.register(new AnnotatedParametersRule());
+
+    Facts facts = new Facts();
+    facts.put("fact1", new Object());
+
+    Map<org.jeasy.rules.api.Rule, Boolean> results = rulesEngine.check(rules, facts);
+
+    for (boolean b : results.values()) {
+      Assertions.assertTrue(b);
+    }
+  }
+
+  @Test
+  public void testMissingFactNotAnnotated() {
+
+    Rules rules = new Rules();
+
+    new AnnotatedParametersRule();
+    rules.register(new AnnotatedParametersRule());
+
+    Facts facts = new Facts();
+    facts.put("fact1", new Object());
+
+    Map<org.jeasy.rules.api.Rule, Boolean> results = rulesEngine.check(rules, facts);
+
+    for (boolean b : results.values()) {
+      Assertions.assertFalse(b);
+    }
+  }
+
+  @Test
+  public void testNoMissingFact() {
+    Rules rules = new Rules();
+    rules.register(
+        new AnnotatedParametersRule() {
+          @Condition
+          public boolean when(@Fact("fact1") Object fact1, @Nullable @Fact("fact2") Object fact2) {
+            return fact1 != null && fact2 != null;
+          }
+        });
+    Facts facts = new Facts();
+    facts.put("fact1", new Object());
+    facts.put("fact2", new Object());
+
+    Map<org.jeasy.rules.api.Rule, Boolean> results = rulesEngine.check(rules, facts);
+
+    for (boolean b : results.values()) {
+      Assertions.assertTrue(b);
+    }
+  }
+
+  @Rule
+  public static class AnnotatedParametersRule {
+
+    @Condition
+    public boolean when(@Fact("fact1") Object fact1, @Nullable @Fact("fact2") Object fact2) {
+      return fact1 != null && fact2 == null;
+    }
+
+    @Action
+    public void then(@Fact("fact1") Object fact1, @Nullable @Fact("fact2") Object fact2) {}
+  }
+}