diff --git a/easy-rules-core/pom.xml b/easy-rules-core/pom.xml
index b3a0faf5..1b88cdf6 100644
--- a/easy-rules-core/pom.xml
+++ b/easy-rules-core/pom.xml
@@ -77,6 +77,11 @@
             <artifactId>mockito-core</artifactId>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.findbugs</groupId>
+            <artifactId>jsr305</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleDefinitionValidator.java b/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleDefinitionValidator.java
index 7511879c..fe34b899 100644
--- a/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleDefinitionValidator.java
+++ b/easy-rules-core/src/main/java/org/jeasy/rules/core/RuleDefinitionValidator.java
@@ -30,7 +30,12 @@
 import java.lang.reflect.Modifier;
 import java.lang.reflect.Parameter;
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
+
 import org.jeasy.rules.annotation.Action;
 import org.jeasy.rules.annotation.Condition;
 import org.jeasy.rules.annotation.Fact;
@@ -117,20 +122,24 @@ private boolean isConditionMethodWellDefined(final Method method) {
                 && validParameters(method);
     }
 
+    private static final Set<String> OTHER_ANNOTATIONS = Collections.singleton("javax.annotation.Nullable");
+
     private boolean validParameters(final Method method) {
         int notAnnotatedParameterCount = 0;
         Annotation[][] parameterAnnotations = method.getParameterAnnotations();
         for (Annotation[] annotations : parameterAnnotations) {
-            if (annotations.length == 0) {
-                notAnnotatedParameterCount += 1;
-            } else {
-                //Annotation types has to be Fact
-                for (Annotation annotation : annotations) {
-                    if (!annotation.annotationType().equals(Fact.class)) {
-                        return false;
-                    }
+            boolean annotatedAsFact = false;
+            for (Annotation annotation : annotations) {
+                //Annotation types has to be Fact or another accepted annotation
+                if (annotation.annotationType().equals(Fact.class)) {
+                    annotatedAsFact = true;
+                } else if (!OTHER_ANNOTATIONS.contains(annotation.annotationType().getCanonicalName())) {
+                    return false;
                 }
             }
+            if (!annotatedAsFact) {
+                notAnnotatedParameterCount += 1;
+            }
         }
         if (notAnnotatedParameterCount > 1) {
             return false;
@@ -147,6 +156,15 @@ private boolean validParameters(final Method method) {
     private Parameter getNotAnnotatedParameter(Method method) {
         Parameter[] parameters = method.getParameters();
         for (Parameter parameter : parameters) {
+            boolean hasAnnotation = false;
+            for (Annotation annotation : parameter.getAnnotations()) {
+                if (annotation.annotationType().equals(Fact.class)) {
+                    hasAnnotation = true;
+                }
+            }
+            if (!hasAnnotation) {
+                return parameter;
+            }
             if (parameter.getAnnotations().length == 0) {
                 return parameter;
             }
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 399ef8ff..437620e0 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
@@ -163,15 +163,23 @@ private List<Object> getActualParameters(Method method, Facts facts) {
         List<Object> actualParameters = new ArrayList<>();
         Annotation[][] parameterAnnotations = method.getParameterAnnotations();
         for (Annotation[] annotations : parameterAnnotations) {
-            if (annotations.length == 1) {
-                String factName = ((Fact) (annotations[0])).value(); //validated upfront.
-                Object fact = facts.get(factName);
-                if (fact == null && !facts.asMap().containsKey(factName)) {
+            String factName = null;
+            boolean annotatedAsNullable = false;
+            for (Annotation annotation : annotations) {
+                if (annotation.annotationType().equals(Fact.class)) {
+                    factName = ((Fact) annotation).value();
+                } else if ("javax.annotation.Nullable".equals(annotation.annotationType().getCanonicalName())) {
+                    annotatedAsNullable = true;
+                }
+            }
+            if (factName != null) {
+                Object fact = facts.get(factName); //validated upfront.
+                if (fact == null && !facts.asMap().containsKey(factName) && !annotatedAsNullable) {
                     throw new NoSuchFactException(format("No fact named '%s' found in known facts: %n%s", factName, facts), factName);
                 }
                 actualParameters.add(fact);
             } else {
-                actualParameters.add(facts); //validated upfront, there may be only one parameter not annotated and which is of type Facts.class
+                actualParameters.add(facts); //validated upfront, there may be only one parameter not annotated as Fact and which is of type Facts.class
             }
         }
         return actualParameters;
diff --git a/easy-rules-core/src/test/java/org/jeasy/rules/core/OptionalFactAnnotationParameterTest.java b/easy-rules-core/src/test/java/org/jeasy/rules/core/OptionalFactAnnotationParameterTest.java
new file mode 100644
index 00000000..7fd171d8
--- /dev/null
+++ b/easy-rules-core/src/test/java/org/jeasy/rules/core/OptionalFactAnnotationParameterTest.java
@@ -0,0 +1,71 @@
+/*
+ * The MIT License
+ *
+ *  Copyright (c) 2021, 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.junit.Assert;
+import org.junit.Test;
+
+import javax.annotation.Nullable;
+import java.util.Map;
+
+/**
+ * Null facts are not accepted by design, a declared fact can be missing though.
+ */
+public class OptionalFactAnnotationParameterTest extends AbstractTest {
+
+    @Test
+    public void testMissingFact() {
+        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()) {
+            Assert.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) {
+        }
+
+    }
+}
diff --git a/licence-header-template.txt b/licence-header-template.txt
index dc24825c..e0431cfc 100644
--- a/licence-header-template.txt
+++ b/licence-header-template.txt
@@ -1,6 +1,6 @@
 The MIT License
 
- Copyright (c) ${currentYear}, Mahmoud Ben Hassine (mahmoud.benhassine@icloud.com)
+ Copyright (c) 2021, 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
diff --git a/pom.xml b/pom.xml
index 426ac55c..469216ea 100644
--- a/pom.xml
+++ b/pom.xml
@@ -37,6 +37,7 @@
         <system-lambda.version>1.1.1</system-lambda.version>
         <slf4j.version>1.7.30</slf4j.version>
         <jackson.version>2.11.3</jackson.version>
+        <jsr305.version>3.0.2</jsr305.version>
         <maven-release-plugin.version>2.5.3</maven-release-plugin.version>
         <maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
         <maven-surefire-plugin.version>2.22.2</maven-surefire-plugin.version>
@@ -112,6 +113,12 @@
                 <version>${mockito.version}</version>
                 <scope>test</scope>
             </dependency>
+            <dependency>
+                <groupId>com.google.code.findbugs</groupId>
+                <artifactId>jsr305</artifactId>
+                <version>${jsr305.version}</version>
+                <scope>test</scope>
+            </dependency>
         </dependencies>
     </dependencyManagement>