diff --git a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt
index 6fac8eec52a..c6e6ba31b4b 100644
--- a/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt
+++ b/compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/SamResolution.kt
@@ -9,6 +9,8 @@ import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.descriptors.EffectiveVisibility
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.caches.NullableMap
+import org.jetbrains.kotlin.fir.caches.getOrPut
 import org.jetbrains.kotlin.fir.containingClassForStaticMemberAttr
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.builder.FirTypeParameterBuilder
@@ -42,7 +44,6 @@ abstract class FirSamResolver {
     abstract fun getSamConstructor(firRegularClass: FirRegularClass): FirSimpleFunction?
 }
 
-private val NULL_STUB = Any()
 val SAM_PARAMETER_NAME = Name.identifier("block")
 
 class FirSamResolverImpl(
@@ -50,9 +51,8 @@ class FirSamResolverImpl(
     private val scopeSession: ScopeSession,
     private val outerClassManager: FirOuterClassManager? = null,
 ) : FirSamResolver() {
-
-    private val resolvedFunctionType: MutableMap<FirRegularClass, Any> = mutableMapOf()
-    private val samConstructor: MutableMap<FirRegularClass, Any> = mutableMapOf()
+    private val resolvedFunctionType: NullableMap<FirRegularClass, ConeLookupTagBasedType?> = NullableMap()
+    private val samConstructor: NullableMap<FirRegularClass, FirSimpleFunction?> = NullableMap()
 
     override fun getFunctionTypeForPossibleSamType(type: ConeKotlinType): ConeKotlinType? {
         return when (type) {
@@ -114,8 +114,8 @@ class FirSamResolverImpl(
 
     override fun getSamConstructor(firRegularClass: FirRegularClass): FirSimpleFunction? {
         return samConstructor.getOrPut(firRegularClass) {
-            buildSamConstructor(firRegularClass) ?: return@getOrPut NULL_STUB
-        } as? FirSimpleFunction
+            buildSamConstructor(firRegularClass)
+        }
     }
 
     private fun buildSamConstructor(firRegularClass: FirRegularClass): FirSimpleFunction? {
@@ -223,12 +223,12 @@ class FirSamResolverImpl(
 
     private fun resolveFunctionTypeIfSamInterface(firRegularClass: FirRegularClass): ConeLookupTagBasedType? {
         return resolvedFunctionType.getOrPut(firRegularClass) {
-            if (!firRegularClass.status.isFun) return@getOrPut NULL_STUB
-            val abstractMethod = firRegularClass.getSingleAbstractMethodOrNull(firSession, scopeSession) ?: return@getOrPut NULL_STUB
+            if (!firRegularClass.status.isFun) return@getOrPut null
+            val abstractMethod = firRegularClass.getSingleAbstractMethodOrNull(firSession, scopeSession) ?: return@getOrPut null
             // TODO: val shouldConvertFirstParameterToDescriptor = samWithReceiverResolvers.any { it.shouldConvertFirstSamParameterToReceiver(abstractMethod) }
 
             abstractMethod.getFunctionTypeForAbstractMethod()
-        } as? ConeLookupTagBasedType
+        }
     }
 
     override fun shouldRunSamConversionForFunction(firFunction: FirFunction): Boolean {
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/caches/NullableMap.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/caches/NullableMap.kt
index 0f1e6788cb1..b12394a31c5 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/caches/NullableMap.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/caches/NullableMap.kt
@@ -12,7 +12,10 @@ import org.jetbrains.kotlin.fir.PrivateForInline
  */
 @OptIn(PrivateForInline::class)
 @JvmInline
-internal value class NullableMap<K, V>(private val map: MutableMap<K, Any> = HashMap()) {
+value class NullableMap<K, V>(
+    @property:PrivateForInline
+    val map: MutableMap<K, Any> = HashMap()
+) {
 
     /**
      * Get value if it is present in map
@@ -31,7 +34,15 @@ internal value class NullableMap<K, V>(private val map: MutableMap<K, Any> = Has
     inline operator fun set(key: K, value: V) {
         map[key] = value ?: NullValue
     }
+
+    @PrivateForInline
+    object NullValue
 }
 
-@PrivateForInline
-internal object NullValue
+inline fun <K, V> NullableMap<K, V>.getOrPut(key: K, defaultValue: () -> V): V {
+    return getOrElse(key) {
+        defaultValue().also {
+            set(key, it)
+        }
+    }
+}