Do not generate underlying classes for enum entries without member declarations.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDelegate.kt

@@ -18,7 +18,6 @@ package org.jetbrains.kotlin.ir.declarations
 
 import org.jetbrains.kotlin.descriptors.VariableDescriptor
 import org.jetbrains.kotlin.ir.*
-import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrExpressionBody
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
@@ -75,6 +74,6 @@ class IrDelegateImpl(
     }
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
-        initializer?.accept(visitor, data)
+        initializer.accept(visitor, data)
     }
 }