diff --git a/api/pom.xml b/api/pom.xml
index 0e1500a..c586b35 100644
--- a/api/pom.xml
+++ b/api/pom.xml
@@ -20,6 +20,19 @@
     <packaging>jar</packaging>
     <name>MapStruct Tools Gem API</name>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
     <build>
         <plugins>
             <plugin>
@@ -71,6 +84,10 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+            </plugin>
             <plugin>
                 <groupId>org.apache.felix</groupId>
                 <artifactId>maven-bundle-plugin</artifactId>
diff --git a/api/src/main/java/org/mapstruct/tools/gem/GemValue.java b/api/src/main/java/org/mapstruct/tools/gem/GemValue.java
index 65f86df..e8b4a5b 100644
--- a/api/src/main/java/org/mapstruct/tools/gem/GemValue.java
+++ b/api/src/main/java/org/mapstruct/tools/gem/GemValue.java
@@ -8,6 +8,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Function;
+import java.util.function.Supplier;
 import javax.lang.model.element.AnnotationMirror;
 import javax.lang.model.element.AnnotationValue;
 import javax.lang.model.element.AnnotationValueVisitor;
@@ -113,6 +114,16 @@ public T getValue() {
         return value;
     }
 
+    /**
+     * Returns the value set by the user, if present, otherwise invoke other and return the result of that invocation.
+     *
+     * @param other a Supplier whose result is returned if no value is present
+     * @return the value  set by the user, if present, otherwise the result of {@code other.get()}
+     */
+    public T getValueOrElseGet(Supplier<T> other) {
+        return value != null ? value : other.get();
+    }
+
     /**
      * The default value, as declared in the annotation
      *
diff --git a/api/src/test/java/org/mapstruct/tools/gem/GemValueTest.java b/api/src/test/java/org/mapstruct/tools/gem/GemValueTest.java
new file mode 100644
index 0000000..b366cde
--- /dev/null
+++ b/api/src/test/java/org/mapstruct/tools/gem/GemValueTest.java
@@ -0,0 +1,195 @@
+/*
+ * Copyright MapStruct Authors.
+ *
+ * Licensed under the Apache License version 2.0, available at https://www.apache.org/licenses/LICENSE-2.0
+ */
+package org.mapstruct.tools.gem;
+
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import javax.lang.model.element.AnnotationValue;
+import javax.lang.model.element.AnnotationValueVisitor;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class GemValueTest {
+
+    static class SimpleAnnotationValue implements AnnotationValue {
+
+        private final int value;
+
+        SimpleAnnotationValue(int value) {
+            this.value = value;
+        }
+
+        @Override
+        public Object getValue() {
+            return value;
+        }
+
+        @Override
+        public <R, P> R accept(AnnotationValueVisitor<R, P> v, P p) {
+            return v.visitInt( value, p );
+        }
+    }
+
+    @Nested
+    class CreateSimpleValueTest {
+
+        @Test
+        void createSimpleValue() {
+            SimpleAnnotationValue annotationValue = new SimpleAnnotationValue(1);
+            GemValue<Integer> gemValue = GemValue.create( annotationValue, new SimpleAnnotationValue(2),
+                    Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isTrue();
+            assertThat( gemValue.hasValue() ).isTrue();
+            assertThat( gemValue.getValue() ).isEqualTo( 1 );
+            assertThat( gemValue.getDefaultValue() ).isEqualTo( 2 );
+            assertThat( gemValue.get() ).as( "get should return value" ).isEqualTo( 1 );
+            assertThat( gemValue.getAnnotationValue() ).isEqualTo( annotationValue );
+            assertThat( gemValue.getValueOrElseGet( () -> 3 ) )
+                    .as( "getValueOrElseGet should return value" ).isEqualTo( 1 );
+        }
+
+        @Test
+        void createSimpleValueWithoutAnnotationValue() {
+            GemValue<Integer> gemValue = GemValue.create( null, new SimpleAnnotationValue(2),
+                    Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isTrue();
+            assertThat( gemValue.hasValue() ).isFalse();
+            assertThat( gemValue.getValue() ).isNull();
+            assertThat( gemValue.getDefaultValue() ).isEqualTo( 2 );
+            assertThat( gemValue.get() ).as( "get should return defaultValue" ).isEqualTo( 2 );
+            assertThat( gemValue.getAnnotationValue() ).isNull();
+            assertThat( gemValue.getValueOrElseGet( () -> 3 ) )
+                    .as( "getValueOrElseGet should return other" ).isEqualTo( 3 );
+        }
+
+        @Test
+        void createSimpleValueWithoutAnnotationDefaultValue() {
+            SimpleAnnotationValue annotationValue = new SimpleAnnotationValue(1);
+            GemValue<Integer> gemValue = GemValue.create( annotationValue, null, Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isTrue();
+            assertThat( gemValue.hasValue() ).isTrue();
+            assertThat( gemValue.getValue() ).isEqualTo( 1 );
+            assertThat( gemValue.getDefaultValue() ).isNull();
+            assertThat( gemValue.get() ).as( "get should return value" ).isEqualTo( 1 );
+            assertThat( gemValue.getAnnotationValue() ).isEqualTo( annotationValue );
+            assertThat( gemValue.getValueOrElseGet( () -> 3 ) )
+                    .as( "getValueOrElseGet should return value" ).isEqualTo( 1 );
+        }
+
+        @Test
+        void createSimpleValueInvalid() {
+            GemValue<Integer> gemValue = GemValue.create( null, null, Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isFalse();
+            assertThat( gemValue.hasValue() ).isFalse();
+            assertThat( gemValue.getValue() ).isNull();
+            assertThat( gemValue.getDefaultValue() ).isNull();
+            assertThat( gemValue.get() ).as( "get should return null" ).isNull();
+            assertThat( gemValue.getAnnotationValue() ).isNull();
+            assertThat( gemValue.getValueOrElseGet( () -> 3 ) )
+                    .as( "getValueOrElseGet should return other" ).isEqualTo( 3 );
+        }
+    }
+
+    static class SimpleArrayAnnotationValue implements AnnotationValue {
+
+        private final List<SimpleAnnotationValue> value;
+
+        SimpleArrayAnnotationValue(int... intValues) {
+            this.value = new ArrayList<>( intValues.length );
+            for ( int v : intValues ) {
+                value.add( new SimpleAnnotationValue( v ) );
+            }
+        }
+
+        @Override
+        public Object getValue() {
+            return value;
+        }
+
+        @Override
+        public <R, P> R accept(AnnotationValueVisitor<R, P> v, P p) {
+            return v.visitArray( value, p );
+        }
+    }
+
+    @Nested
+    class CreateArrayTest {
+
+        @Test
+        void createArrayValue() {
+            SimpleArrayAnnotationValue annotationValue = new SimpleArrayAnnotationValue(1);
+            GemValue<List<Integer>> gemValue = GemValue.createArray( annotationValue,
+                    new SimpleArrayAnnotationValue(2), Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isTrue();
+            assertThat( gemValue.hasValue() ).isTrue();
+            assertThat( gemValue.getValue() ).isEqualTo( Collections.singletonList( 1 ) );
+            assertThat( gemValue.getDefaultValue() ).isEqualTo( Collections.singletonList( 2 ) );
+            assertThat( gemValue.get() ).as( "get should return value" ).isEqualTo(
+                    Collections.singletonList( 1 ) );
+            assertThat( gemValue.getAnnotationValue() ).isEqualTo( annotationValue );
+            assertThat( gemValue.getValueOrElseGet( Collections::emptyList ) )
+                    .as( "getValueOrElseGet should return value" )
+                    .isEqualTo( Collections.singletonList( 1 ) );
+        }
+
+        @Test
+        void createArrayValueWithoutAnnotationValue() {
+            GemValue<List<Integer>> gemValue = GemValue.createArray( null,
+                    new SimpleArrayAnnotationValue(2), Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isTrue();
+            assertThat( gemValue.hasValue() ).isFalse();
+            assertThat( gemValue.getValue() ).isNull();
+            assertThat( gemValue.getDefaultValue() ).isEqualTo( Collections.singletonList( 2 ) );
+            assertThat( gemValue.get() ).as( "get should return defaultValue" )
+                    .isEqualTo( Collections.singletonList( 2 ) );
+            assertThat( gemValue.getAnnotationValue() ).isNull();
+            assertThat( gemValue.getValueOrElseGet( Collections::emptyList ) )
+                    .as( "getValueOrElseGet should return other" ).isEqualTo( Collections.emptyList() );
+        }
+
+        @Test
+        void createArrayValueWithoutAnnotationDefaultValue() {
+            SimpleArrayAnnotationValue annotationValue = new SimpleArrayAnnotationValue(1);
+            GemValue<List<Integer>> gemValue = GemValue.createArray( annotationValue, null, Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isTrue();
+            assertThat( gemValue.hasValue() ).isTrue();
+            assertThat( gemValue.getValue() ).isEqualTo( Collections.singletonList( 1 ) );
+            assertThat( gemValue.getDefaultValue() ).isNull();
+            assertThat( gemValue.get() ).as( "get should return value" )
+                    .isEqualTo( Collections.singletonList( 1 ) );
+            assertThat( gemValue.getAnnotationValue() ).isEqualTo( annotationValue );
+            assertThat( gemValue.getValueOrElseGet( Collections::emptyList ) )
+                    .as( "getValueOrElseGet should return value" )
+                    .isEqualTo( Collections.singletonList( 1 ) );
+        }
+
+        @Test
+        void createArrayValueInvalid() {
+            GemValue<List<Integer>> gemValue = GemValue.createArray( null, null, Integer.class );
+            assertThat( gemValue ).isNotNull();
+            assertThat( gemValue.isValid() ).isFalse();
+            assertThat( gemValue.hasValue() ).isFalse();
+            assertThat( gemValue.getValue() ).isNull();
+            assertThat( gemValue.getDefaultValue() ).isNull();
+            assertThat( gemValue.get() ).as( "get should return null" ).isNull();
+            assertThat( gemValue.getAnnotationValue() ).isNull();
+            assertThat( gemValue.getValueOrElseGet( () -> Collections.singletonList( 3 ) ) )
+                    .as( "getValueOrElseGet should return other" ).isEqualTo( Collections.singletonList( 3 ) );
+        }
+    }
+}