Add check & unit tests in case the feature value is a collection impl

lib/src/main/java/growthbook/sdk/java/FeatureEvaluator.java

@@ -303,6 +303,8 @@ public <ValueType> FeatureResult<ValueType> evaluateFeature(
                     if (featureUsageCallback != null) {
                         featureUsageCallback.onFeatureUsage(key, forcedRuleFeatureValue);
                     }
+
+                    goOutFromCircularLoop();
                     return forcedRuleFeatureValue;
                 } else {
 
@@ -419,4 +421,9 @@ public <ValueType> FeatureResult<ValueType> evaluateFeature(
             return null;
         }
     }
+
+    private void goOutFromCircularLoop() {
+        featureEvalContext.setId(null);
+        featureEvalContext.getEvaluatedFeatures().clear();
+    }
 }

lib/src/main/java/growthbook/sdk/java/FeatureResult.java

@@ -9,6 +9,8 @@
 import lombok.Builder;
 import lombok.Data;
 import javax.annotation.Nullable;
+import java.lang.reflect.Type;
+import java.util.Collection;
 
 /**
  * Results for a {@link FeatureEvaluator#evaluateFeature(String, GBContext, Class, JsonObject)}
@@ -82,6 +84,10 @@ public Boolean isOn() {
             return (Double) value != 0;
         }
 
+        if (value instanceof Collection<?>) {
+            return !((Collection<?>) value).isEmpty();
+        }
+
         return false;
     }
 

lib/src/test/java/growthbook/sdk/java/FeatureResultTest.java

@@ -1,12 +1,17 @@
 package growthbook.sdk.java;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNull;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 
 import org.junit.jupiter.api.Test;
 
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+
 class FeatureResultTest {
     @Test
     void canBeConstructed() {
@@ -169,5 +174,47 @@ void featureResult_isOn_withEmptyValue_returnsFalse_forStrings() {
         assertTrue(subject.isOff());
     }
 
+    @Test
+    void featureResult_isOn_withPerceivedNotEmptyCollection() {
+        FeatureResult<Object> subject = FeatureResult
+                .builder()
+                .value(Collections.singleton("acme"))
+                .build();
+
+        assertTrue(subject.isOn());
+        assertFalse(subject.isOff());
+    }
+
+    @Test
+    void featureResult_isOff_withPerceivedEmptyCollection() {
+        FeatureResult<Object> subject = FeatureResult
+                .builder()
+                .value(Collections.emptyList())
+                .build();
+
+        assertFalse(subject.isOn());
+        assertTrue(subject.isOff());
+    }
+
+    @Test
+    void proofOfConceptCollectionTest() {
+        GBContext ctx = GBContext.builder()
+            .featuresJson(
+                "{\"test\":{\"defaultValue\":[],\"rules\":[{\"force\":[\"line1\",\"line2\"]}]}}")
+            .build();
+
+        GrowthBook growthBook = new GrowthBook(ctx);
+
+        String featureName = "test";
+
+        assertTrue(growthBook.isOn(featureName));
+        assertFalse(growthBook.isOff(featureName));
+
+        Object value = growthBook.getFeatureValue(featureName, new ArrayList<>());
+
+        assertInstanceOf(Collection.class, value);
+        assertFalse(((Collection<?>) value).isEmpty());
+    }
+
     // endregion isOn() isOff()
 }