diff --git a/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/PsiConversionUtils.kt b/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/PsiConversionUtils.kt
index be6147c605d..3c05ac4e327 100644
--- a/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/PsiConversionUtils.kt
+++ b/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/PsiConversionUtils.kt
@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.expressions.builder.*
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.types.FirTypeRef
-import org.jetbrains.kotlin.fir.types.builder.buildImplicitTypeRef
+import org.jetbrains.kotlin.fir.types.impl.FirImplicitTypeRefImplWithoutSource
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.psi.*
 
@@ -94,9 +94,7 @@ internal fun generateTemporaryVariable(
         this.source = source
         this.moduleData = moduleData
         origin = FirDeclarationOrigin.Source
-        returnTypeRef = typeRef ?: buildImplicitTypeRef {
-            this.source = source
-        }
+        returnTypeRef = typeRef ?: FirImplicitTypeRefImplWithoutSource
         this.name = name
         this.initializer = initializer
         symbol = FirPropertySymbol(name)
diff --git a/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt b/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt
index 57531d6d733..d4660cf4c45 100644
--- a/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt
+++ b/compiler/fir/raw-fir/psi2fir/src/org/jetbrains/kotlin/fir/builder/RawFirBuilder.kt
@@ -240,9 +240,7 @@ open class RawFirBuilder(
             valueParameter.toFirValueParameter(defaultTypeRef, functionSymbol, valueParameterDeclaration, additionalAnnotations)
 
         private fun KtTypeReference?.toFirOrImplicitType(): FirTypeRef =
-            convertSafe() ?: buildImplicitTypeRef {
-                source = this@toFirOrImplicitType?.toFirSourceElement(KtFakeSourceElementKind.ImplicitTypeRef)
-            }
+            this?.toFirOrErrorType() ?: FirImplicitTypeRefImplWithoutSource
 
         private fun KtTypeReference?.toFirOrUnitType(): FirTypeRef =
             convertSafe() ?: implicitUnitType
diff --git a/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/builder/FirImplicitTypeRefBuilder.kt b/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/builder/FirImplicitTypeRefBuilder.kt
index 29c7eff3c78..ae57b681db6 100644
--- a/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/builder/FirImplicitTypeRefBuilder.kt
+++ b/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/builder/FirImplicitTypeRefBuilder.kt
@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.fir.visitors.*
 
 @FirBuilderDsl
 class FirImplicitTypeRefBuilder {
-    var source: KtSourceElement? = null
+    lateinit var source: KtSourceElement
 
     fun build(): FirImplicitTypeRef {
         return FirImplicitTypeRefImpl(
@@ -34,7 +34,7 @@ class FirImplicitTypeRefBuilder {
 }
 
 @OptIn(ExperimentalContracts::class)
-inline fun buildImplicitTypeRef(init: FirImplicitTypeRefBuilder.() -> Unit = {}): FirImplicitTypeRef {
+inline fun buildImplicitTypeRef(init: FirImplicitTypeRefBuilder.() -> Unit): FirImplicitTypeRef {
     contract {
         callsInPlace(init, kotlin.contracts.InvocationKind.EXACTLY_ONCE)
     }
@@ -42,11 +42,11 @@ inline fun buildImplicitTypeRef(init: FirImplicitTypeRefBuilder.() -> Unit = {})
 }
 
 @OptIn(ExperimentalContracts::class)
-inline fun buildImplicitTypeRefCopy(original: FirImplicitTypeRef, init: FirImplicitTypeRefBuilder.() -> Unit = {}): FirImplicitTypeRef {
+inline fun buildImplicitTypeRefCopy(original: FirImplicitTypeRef, init: FirImplicitTypeRefBuilder.() -> Unit): FirImplicitTypeRef {
     contract {
         callsInPlace(init, kotlin.contracts.InvocationKind.EXACTLY_ONCE)
     }
     val copyBuilder = FirImplicitTypeRefBuilder()
-    copyBuilder.source = original.source
+    original.source?.let { copyBuilder.source = it }
     return copyBuilder.apply(init).build()
 }
diff --git a/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/impl/FirImplicitTypeRefImpl.kt b/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/impl/FirImplicitTypeRefImpl.kt
index 37d1354a25f..e268b8288f2 100644
--- a/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/impl/FirImplicitTypeRefImpl.kt
+++ b/compiler/fir/tree/gen/org/jetbrains/kotlin/fir/types/impl/FirImplicitTypeRefImpl.kt
@@ -20,7 +20,7 @@ import org.jetbrains.kotlin.fir.builder.toMutableOrEmpty
  */
 
 internal class FirImplicitTypeRefImpl(
-    override val source: KtSourceElement?,
+    override val source: KtSourceElement,
 ) : FirImplicitTypeRef() {
     override val annotations: List<FirAnnotation> get() = emptyList()
 
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirGeneration.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirGeneration.kt
index ee1d6113d36..3e383973f01 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirGeneration.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirGeneration.kt
@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.fir.references.builder.buildResolvedNamedReference
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.types.builder.buildImplicitTypeRef
+import org.jetbrains.kotlin.fir.types.impl.FirImplicitTypeRefImplWithoutSource
 import org.jetbrains.kotlin.name.Name
 
 fun FirVariable.toQualifiedAccess(
@@ -51,9 +52,7 @@ fun generateTemporaryVariable(
         this.source = source
         this.moduleData = moduleData
         origin = FirDeclarationOrigin.Source
-        returnTypeRef = typeRef ?: buildImplicitTypeRef {
-            this.source = source
-        }
+        returnTypeRef = typeRef ?: FirImplicitTypeRefImplWithoutSource
         this.name = name
         this.initializer = initializer
         symbol = FirPropertySymbol(name)
diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/Utils.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/Utils.kt
index ee1f45e0191..9161aaf26fd 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/Utils.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/Utils.kt
@@ -52,9 +52,9 @@ fun <R : FirTypeRef> R.copyWithNewSource(newSource: KtSourceElement?): R {
             qualifier += typeRef.qualifier
             annotations += typeRef.annotations
         }
-        is FirImplicitTypeRef -> buildImplicitTypeRefCopy(typeRef) {
-            source = newSource
-        }
+        is FirImplicitTypeRef -> newSource?.let {
+            buildImplicitTypeRefCopy(typeRef) { source = it }
+        } ?: FirImplicitTypeRefImplWithoutSource
         is FirFunctionTypeRefImpl -> buildFunctionTypeRefCopy(typeRef) {
             source = newSource
         }
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt
index 31470cdade6..622fb7de9c1 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt
@@ -482,6 +482,9 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
         impl(functionTypeRef)
         impl(implicitTypeRef) {
             defaultEmptyList("annotations")
+            default("source") {
+                notNull = true
+            }
         }
 
         impl(reference, "FirStubReference") {
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractBuilderConfigurator.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractBuilderConfigurator.kt
index b85ee602264..c32dd704c1e 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractBuilderConfigurator.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractBuilderConfigurator.kt
@@ -69,9 +69,11 @@ abstract class AbstractBuilderConfigurator<T : AbstractFirTreeBuilder>(val firTr
 
         inner class DefaultValueContext(private val field: FieldWithDefault) {
             var value: String? = null
+            var notNull: Boolean? = null
 
             fun applyConfiguration() {
                 if (value != null) field.defaultValueInBuilder = value
+                if (notNull != null) field.notNull = notNull!!
             }
         }
     }
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractFirTreeImplementationConfigurator.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractFirTreeImplementationConfigurator.kt
index 169841f86e8..fad9ad1b869 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractFirTreeImplementationConfigurator.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/context/AbstractFirTreeImplementationConfigurator.kt
@@ -217,11 +217,17 @@ abstract class AbstractFirTreeImplementationConfigurator {
 
             var needAcceptAndTransform: Boolean = true
 
+            var notNull: Boolean = false
+
             fun applyConfiguration() {
                 field.withGetter = withGetter
                 field.customSetter = customSetter
                 isMutable?.let { field.isMutable = it }
                 field.needAcceptAndTransform = needAcceptAndTransform
+
+                if (notNull) {
+                    field.notNull = true
+                }
                 when {
                     value != null -> field.defaultValueInImplementation = value
                     delegate != null -> {
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt
index 65e13576199..1c8dc61f1bf 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt
@@ -30,6 +30,7 @@ sealed class Field : Importable {
 
     open val overridenTypes: MutableSet<Importable> = mutableSetOf()
     open var useNullableForReplace: Boolean = false
+    open var notNull: Boolean = false
 
     var withBindThis = true
 
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/builder.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/builder.kt
index 113696f2d89..86f33117c57 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/builder.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/builder.kt
@@ -129,7 +129,7 @@ private fun SmartPrinter.printBuilder(builder: Builder) {
 
 
 private val String.nullable: String get() = if (endsWith("?")) this else "$this?"
-private fun FieldWithDefault.needBackingField(fieldIsUseless: Boolean) = !nullable && origin !is FieldList && if (fieldIsUseless) {
+private fun FieldWithDefault.needBackingField(fieldIsUseless: Boolean) = (!nullable || notNull) && origin !is FieldList && if (fieldIsUseless) {
     defaultValueInImplementation == null
 } else {
     defaultValueInBuilder == null
@@ -145,7 +145,7 @@ private fun SmartPrinter.printFieldInBuilder(field: FieldWithDefault, builder: B
         return true to false
     }
     val name = field.name
-    val type = field.typeWithArguments
+    val type = field.getTypeWithArguments(field.notNull)
     val defaultValue = if (fieldIsUseless)
         field.defaultValueInImplementation.also { requireNotNull(it) }
     else
@@ -305,6 +305,7 @@ private fun SmartPrinter.printDslBuildCopyFunction(
             when {
                 field.origin is FieldList -> println("copyBuilder.${field.name}.addAll(original.${field.name})")
                 field.type == declarationAttributesType.type -> println("copyBuilder.${field.name} = original.${field.name}.copy()")
+                field.notNull -> println("original.${field.name}?.let { copyBuilder.${field.name} = it }")
                 else -> println("copyBuilder.${field.name} = original.${field.name}")
             }
         }
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/field.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/field.kt
index 13e5998f339..44eebbe9e32 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/field.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/field.kt
@@ -10,7 +10,7 @@ import org.jetbrains.kotlin.fir.tree.generator.model.SimpleField
 import org.jetbrains.kotlin.util.SmartPrinter
 
 
-fun SmartPrinter.printField(field: Field, isImplementation: Boolean, override: Boolean, end: String) {
+fun SmartPrinter.printField(field: Field, isImplementation: Boolean, override: Boolean, end: String, notNull: Boolean = false) {
     if (isImplementation && !field.isVal && field.isVolatile) {
         println("@Volatile")
     }
@@ -22,7 +22,7 @@ fun SmartPrinter.printField(field: Field, isImplementation: Boolean, override: B
     } else {
         print("var")
     }
-    val type = if (isImplementation) field.getMutableType() else field.typeWithArguments
+    val type = if (isImplementation) field.getMutableType(notNull = notNull) else field.getTypeWithArguments(notNull = notNull)
     println(" ${field.name}: $type$end")
 }
 
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/implementation.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/implementation.kt
index 314e64e3df7..90f968a81d6 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/implementation.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/implementation.kt
@@ -77,7 +77,7 @@ fun SmartPrinter.printImplementation(implementation: Implementation) {
             withIndent {
 
                 fieldsWithoutDefault.forEachIndexed { _, field ->
-                    printField(field, isImplementation = true, override = true, end = ",")
+                    printField(field, isImplementation = true, override = true, end = ",", notNull = field.notNull)
                 }
             }
             print(")")
@@ -94,7 +94,7 @@ fun SmartPrinter.printImplementation(implementation: Implementation) {
                 allFields.forEach {
 
                     abstract()
-                    printField(it, isImplementation = true, override = true, end = "")
+                    printField(it, isImplementation = true, override = true, end = "", notNull = it.notNull)
                 }
             } else {
                 fieldsWithDefault.forEach {
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/utils.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/utils.kt
index 15e7f29a478..63b761f8f4e 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/utils.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/utils.kt
@@ -122,14 +122,14 @@ fun Field.replaceFunctionDeclaration(overridenType: Importable? = null, forceNul
     return "fun replace$capName(new$capName: $typeWithNullable)"
 }
 
-fun Field.getMutableType(forBuilder: Boolean = false): String = when (this) {
+fun Field.getMutableType(forBuilder: Boolean = false, notNull: Boolean = false): String = when (this) {
     is FieldList -> when {
         isMutableOrEmpty && !forBuilder -> "MutableOrEmpty$typeWithArguments"
         isMutable -> "Mutable$typeWithArguments"
         else -> typeWithArguments
     }
-    is FieldWithDefault -> if (isMutable) origin.getMutableType() else typeWithArguments
-    else -> typeWithArguments
+    is FieldWithDefault -> if (isMutable) origin.getMutableType(notNull) else getTypeWithArguments(notNull)
+    else -> getTypeWithArguments(notNull)
 }
 
 fun Field.call(): String = if (nullable) "?." else "."
@@ -151,18 +151,19 @@ fun Kind?.braces(): String = when (this) {
 
 val Element.safeDecapitalizedName: String get() = if (name == "Class") "klass" else name.replaceFirstChar(Char::lowercaseChar)
 
-val Importable.typeWithArguments: String
-    get() = when (this) {
-        is AbstractElement -> type + generics
-        is Implementation -> type + element.generics
-        is FirField -> element.typeWithArguments + if (nullable) "?" else ""
-        is Field -> type + generics + if (nullable) "?" else ""
-        is Type -> type + generics
-        is ImplementationWithArg -> type + generics
-        is LeafBuilder -> type + implementation.element.generics
-        is IntermediateBuilder -> type
-        else -> throw IllegalArgumentException()
-    }
+val Importable.typeWithArguments: String get() = getTypeWithArguments()
+
+fun Importable.getTypeWithArguments(notNull: Boolean = false): String = when (this) {
+    is AbstractElement -> type + generics
+    is Implementation -> type + element.generics
+    is FirField -> element.getTypeWithArguments(notNull) + if (nullable && !notNull) "?" else ""
+    is Field -> type + generics + if (nullable && !notNull) "?" else ""
+    is Type -> type + generics
+    is ImplementationWithArg -> type + generics
+    is LeafBuilder -> type + implementation.element.generics
+    is IntermediateBuilder -> type
+    else -> throw IllegalArgumentException()
+}
 
 val ImplementationWithArg.generics: String
     get() = argument?.let { "<${it.type}>" } ?: ""