From 920d15ae0a7884a9d0144bd8f4dcad605eb17213 Mon Sep 17 00:00:00 2001
From: IlyaMuravjov <muravjovilya@gmail.com>
Date: Tue, 25 Jul 2023 17:29:21 +0300
Subject: [PATCH] Make Java fuzzer fallback to `null` value when nothing else
 works

---
 .../org/utbot/engine/UtBotSymbolicEngine.kt       |  2 ++
 .../kotlin/org/utbot/fuzzing/providers/Objects.kt | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/utbot-framework/src/main/kotlin/org/utbot/engine/UtBotSymbolicEngine.kt b/utbot-framework/src/main/kotlin/org/utbot/engine/UtBotSymbolicEngine.kt
index 46d16f234d..822896b447 100644
--- a/utbot-framework/src/main/kotlin/org/utbot/engine/UtBotSymbolicEngine.kt
+++ b/utbot-framework/src/main/kotlin/org/utbot/engine/UtBotSymbolicEngine.kt
@@ -43,6 +43,7 @@ import org.utbot.framework.util.graph
 import org.utbot.framework.util.sootMethod
 import org.utbot.fuzzer.*
 import org.utbot.fuzzing.*
+import org.utbot.fuzzing.providers.AnyDepthNullValueProvider
 import org.utbot.fuzzing.utils.Trie
 import org.utbot.instrumentation.ConcreteExecutor
 import org.utbot.instrumentation.instrumentation.Instrumentation
@@ -392,6 +393,7 @@ class UtBotSymbolicEngine(
             emit(UtError(e.message ?: "Failed to create ValueProvider", e))
             return@flow
         }.let(transform)
+            .withFallback(AnyDepthNullValueProvider)
 
         val coverageToMinStateBeforeSize = mutableMapOf<Trie.Node<Instruction>, Int>()
 
diff --git a/utbot-java-fuzzing/src/main/kotlin/org/utbot/fuzzing/providers/Objects.kt b/utbot-java-fuzzing/src/main/kotlin/org/utbot/fuzzing/providers/Objects.kt
index 77612897c9..528541cfd6 100644
--- a/utbot-java-fuzzing/src/main/kotlin/org/utbot/fuzzing/providers/Objects.kt
+++ b/utbot-java-fuzzing/src/main/kotlin/org/utbot/fuzzing/providers/Objects.kt
@@ -132,6 +132,21 @@ object NullValueProvider : ValueProvider<FuzzedType, FuzzedValue, FuzzedDescript
     }
 }
 
+/**
+ * Unlike [NullValueProvider] can generate `null` values at any depth.
+ *
+ * Intended to be used as a last fallback.
+ */
+object AnyDepthNullValueProvider : ValueProvider<FuzzedType, FuzzedValue, FuzzedDescription> {
+
+    override fun accept(type: FuzzedType) = type.classId.isRefType
+
+    override fun generate(
+        description: FuzzedDescription,
+        type: FuzzedType
+    ) = sequenceOf<Seed<FuzzedType, FuzzedValue>>(Seed.Simple(nullFuzzedValue(classClassId)))
+}
+
 /**
  * Finds and create object from implementations of abstract classes or interfaces.
  */