Raw FIR: set val setter to null instead of default one

compiler/fir/tree/src/org/jetbrains/kotlin/fir/FirRenderer.kt

@@ -350,8 +350,8 @@ class FirRenderer(builder: StringBuilder) : FirVisitorVoid() {
             println()
         }
         if (property.isVar) {
-            property.setter.accept(this)
-            if (property.setter.body == null) {
+            property.setter?.accept(this)
+            if (property.setter?.body == null) {
                 println()
             }
         }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/FirProperty.kt

@@ -22,7 +22,7 @@ interface FirProperty : @VisitedSupertype FirDeclaration, FirCallableMemberDecla
     // Should it be nullable or have some default?
     val getter: FirPropertyAccessor
 
-    val setter: FirPropertyAccessor
+    val setter: FirPropertyAccessor?
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R =
         visitor.visitProperty(this, data)
@@ -32,6 +32,6 @@ interface FirProperty : @VisitedSupertype FirDeclaration, FirCallableMemberDecla
         initializer?.accept(visitor, data)
         delegate?.accept(visitor, data)
         getter.accept(visitor, data)
-        setter.accept(visitor, data)
+        setter?.accept(visitor, data)
     }
 }

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/impl/FirMemberPropertyImpl.kt

@@ -36,7 +36,7 @@ class FirMemberPropertyImpl(
     override val isVar: Boolean,
     override var initializer: FirExpression?,
     override var getter: FirPropertyAccessor,
-    override var setter: FirPropertyAccessor,
+    override var setter: FirPropertyAccessor?,
     override var delegate: FirExpression?
 ) : FirAbstractCallableMember(
     session, psi, name, visibility, modality, isExpect, isActual, isOverride, receiverTypeRef, returnTypeRef
@@ -49,7 +49,7 @@ class FirMemberPropertyImpl(
 
     override fun <D> transformChildren(transformer: FirTransformer<D>, data: D): FirElement {
         getter = getter.transformSingle(transformer, data)
-        setter = setter.transformSingle(transformer, data)
+        setter = setter?.transformSingle(transformer, data)
         initializer = initializer?.transformSingle(transformer, data)
         delegate = delegate?.transformSingle(transformer, data)