Data builders: fix nullable fields of composite type (#6855)

* Add a nullable field

* Data builders: fix nullable composite objects

* Update test fixtures

Author: martinbonnin

libraries/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/codegen/kotlin/KotlinResolver.kt

@@ -134,7 +134,7 @@ internal class KotlinResolver(
     return when (type) {
       is IrNonNullType2 -> resolveIrType2(type.ofType).copy(nullable = false)
       is IrListType2 -> KotlinSymbols.List.parameterizedBy(resolveIrType2(type.ofType)).copy(nullable = true)
-      is IrCompositeType2 -> mapTypes.get(type.name) ?: error("Cannot find map type for ${type.name}")
+      is IrCompositeType2 -> mapTypes.get(type.name)?.copy(nullable = true) ?: error("Cannot find map type for ${type.name}")
       is IrEnumType2 -> resolveIrType(IrEnumType(type.name, nullable = true), false).copy(nullable = true)
       is IrScalarType2 -> resolveIrType(IrScalarType(type.name, nullable = true), false).copy(nullable = true)
     }

libraries/apollo-compiler/src/main/kotlin/com/apollographql/apollo/compiler/codegen/kotlin/builders/DataBuilderBuilder.kt

@@ -93,7 +93,7 @@ internal class DataBuilderBuilder(
              * If this is a concrete type, initialize typename directly. If not, the user must provide it
              */
             addInitializerBlock(buildCodeBlock {
-              add("__typename = %S", dataBuilder.name)
+              add("__typename = %S\n", dataBuilder.name)
             })
           }
         }