perf: avoid ImmutableStructure allocation for empty ImmutableContext

src/main/java/dev/openfeature/sdk/ImmutableContext.java

@@ -2,7 +2,6 @@
 
 import dev.openfeature.sdk.internal.ExcludeFromGeneratedCoverageReport;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Function;
 import lombok.ToString;
@@ -32,7 +31,7 @@ public final class ImmutableContext implements EvaluationContext {
      * provided.
      */
     public ImmutableContext() {
-        this(new HashMap<>());
+        this(Collections.emptyMap());
     }
 
     /**
@@ -41,7 +40,7 @@ public ImmutableContext() {
      * @param targetingKey targeting key
      */
     public ImmutableContext(String targetingKey) {
-        this(targetingKey, new HashMap<>());
+        this(targetingKey, Collections.emptyMap());
     }
 
     /**
@@ -63,6 +62,8 @@ public ImmutableContext(Map<String, Value> attributes) {
     public ImmutableContext(String targetingKey, Map<String, Value> attributes) {
         if (targetingKey != null) {
             this.structure = new ImmutableStructure(targetingKey, attributes);
+        } else if (attributes == null || attributes.isEmpty()) {
+            this.structure = ImmutableStructure.EMPTY;
         } else {
             this.structure = new ImmutableStructure(attributes);
         }

src/main/java/dev/openfeature/sdk/ImmutableStructure.java

@@ -1,5 +1,6 @@
 package dev.openfeature.sdk;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -21,6 +22,8 @@
 @SuppressWarnings({"PMD.BeanMembersShouldSerialize", "checkstyle:MissingJavadocType"})
 public final class ImmutableStructure extends AbstractStructure {
 
+    static final ImmutableStructure EMPTY = new ImmutableStructure(Collections.emptyMap());
+
     /**
      * create an immutable structure with the empty attributes.
      */

src/test/java/dev/openfeature/sdk/ImmutableContextTest.java

@@ -1,6 +1,7 @@
 package dev.openfeature.sdk;
 
 import static dev.openfeature.sdk.EvaluationContext.TARGETING_KEY;
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotEquals;
@@ -216,6 +217,42 @@ void immutableContextHashCodeIsStable() {
         assertEquals(first, second);
     }
 
+    @Nested
+    @DisplayName("ImmutableContext(String, Map) branch logic")
+    class ConstructorBranches {
+
+        @Test
+        @DisplayName("non-null targeting key with empty attributes is preserved")
+        void nonNullTargetingKeyWithEmptyAttributesIsPreserved() {
+            ImmutableContext ctx = new ImmutableContext("key", Collections.emptyMap());
+            assertThat(ctx.getTargetingKey()).isEqualTo("key");
+            assertThat(ctx.keySet()).contains(TARGETING_KEY);
+        }
+
+        @Test
+        @DisplayName("non-null targeting key with null attributes is preserved")
+        void nonNullTargetingKeyWithNullAttributesIsPreserved() {
+            ImmutableContext ctx = new ImmutableContext("key", null);
+            assertThat(ctx.getTargetingKey()).isEqualTo("key");
+        }
+
+        @Test
+        @DisplayName("null targeting key with empty attributes yields empty context")
+        void nullTargetingKeyWithEmptyAttributesYieldsEmptyContext() {
+            ImmutableContext ctx = new ImmutableContext((String) null, Collections.emptyMap());
+            assertThat(ctx.getTargetingKey()).isNull();
+            assertThat(ctx.isEmpty()).isTrue();
+        }
+
+        @Test
+        @DisplayName("null targeting key with null attributes yields empty context")
+        void nullTargetingKeyWithNullAttributesYieldsEmptyContext() {
+            ImmutableContext ctx = new ImmutableContext((String) null, null);
+            assertThat(ctx.getTargetingKey()).isNull();
+            assertThat(ctx.isEmpty()).isTrue();
+        }
+    }
+
     @Nested
     class Equals {
         ImmutableContext ctx = new ImmutableContext("c", Map.of("a", new Value("b")));