diff --git a/Sources/Apollo/GraphQLExecutor.swift b/Sources/Apollo/GraphQLExecutor.swift
index ac7e83b803..1d4b2b684b 100644
--- a/Sources/Apollo/GraphQLExecutor.swift
+++ b/Sources/Apollo/GraphQLExecutor.swift
@@ -286,7 +286,7 @@ final class GraphQLExecutor {
         }
 
       case let .typeCase(typeCase):
-        #warning("Write extensive tests for this.")
+        #warning("Write extensive tests for this. Multiple merged sibling type cases.")
         if let runtimeType = runtimeType, runtimeType._canBeConverted(to: typeCase.typeCondition) {
           try groupFields(typeCase.selectionSet.selections,
                           forRuntimeType: runtimeType,
@@ -390,10 +390,18 @@ final class GraphQLExecutor {
             elementFieldInfo.cachePath.append(indexSegment)
           }
 
-          return self.complete(fields: elementFieldInfo,
-                               withValue: element,
-                               asType: innerType,
-                               accumulator: accumulator)
+          return self
+            .complete(fields: elementFieldInfo,
+                      withValue: element,
+                      asType: innerType,
+                      accumulator: accumulator)
+            .mapError { error in
+              if !(error is GraphQLResultError) {
+                return GraphQLResultError(path: elementFieldInfo.responsePath, underlying: error)
+              } else {
+                return error
+              }
+            }
         }
 
       return lazilyEvaluateAll(completedArray).map {
diff --git a/Sources/ApolloAPI/CodegenV1/GraphQLEnum.swift b/Sources/ApolloAPI/CodegenV1/GraphQLEnum.swift
index b1895ee047..6ef3e7b22e 100644
--- a/Sources/ApolloAPI/CodegenV1/GraphQLEnum.swift
+++ b/Sources/ApolloAPI/CodegenV1/GraphQLEnum.swift
@@ -52,7 +52,7 @@ where T: RawRepresentable & CaseIterable, T.RawValue == String {
 extension GraphQLEnum: CustomScalarType {
   public init(jsonValue: JSONValue) throws {
     guard let stringData = jsonValue as? String else {
-      throw CacheError.Reason.unrecognizedCacheData(jsonValue, forType: Self.self)
+      throw JSONDecodingError.couldNotConvert(value: jsonValue, to: String.self)      
     }
     self.init(rawValue: stringData)
   }
diff --git a/Sources/ApolloAPI/ScalarTypes.swift b/Sources/ApolloAPI/ScalarTypes.swift
index 5a3d311f4b..8a36a09cdb 100644
--- a/Sources/ApolloAPI/ScalarTypes.swift
+++ b/Sources/ApolloAPI/ScalarTypes.swift
@@ -21,6 +21,7 @@ extension ScalarType {
   public var asInputValue: InputValue { .scalar(self) }
 }
 
+#warning("TODO: do we really need to have both scalar and custom scalar?")
 public protocol CustomScalarType:
   AnyScalarType,
   JSONDecodable,
@@ -36,5 +37,7 @@ extension CustomScalarType {
     try Self.init(jsonValue: cacheData)
   }
 
-  @inlinable public static var asOutputType: Selection.Field.OutputType { .customScalar(self) }
+  @inlinable public static var asOutputType: Selection.Field.OutputType {
+    .nonNull(.customScalar(self))
+  }
 }
diff --git a/Tests/ApolloTests/GraphQLExecutor_SelectionSetMapper_FromResponse_Tests.swift b/Tests/ApolloTests/GraphQLExecutor_SelectionSetMapper_FromResponse_Tests.swift
index 3e1a75f2a3..7c197c7ab5 100644
--- a/Tests/ApolloTests/GraphQLExecutor_SelectionSetMapper_FromResponse_Tests.swift
+++ b/Tests/ApolloTests/GraphQLExecutor_SelectionSetMapper_FromResponse_Tests.swift
@@ -137,7 +137,7 @@ class GraphQLExecutor_SelectionSetMapper_FromResponse_Tests: XCTestCase {
     class GivenSelectionSet: MockSelectionSet {
       override class var selections: [Selection] { [Selection.field("name", String?.self)] }
     }
-    let object: JSONObject = ["name": "Luke Skywalker"]
+    let object: JSONObject = [:]
 
     // when
     XCTAssertThrowsError(try readValues(GivenSelectionSet.self, from: object)) { (error) in
@@ -257,7 +257,9 @@ class GraphQLExecutor_SelectionSetMapper_FromResponse_Tests: XCTestCase {
   func test__nonnull_enum__givenDataHasNullValueForField_throwsNullValueError() {
     // given
     class GivenSelectionSet: MockSelectionSet {
-      override class var selections: [Selection] { [Selection.field("size", GraphQLEnum<MockEnum>.self)] }
+      override class var selections: [Selection] {[
+        Selection.field("size", GraphQLEnum<MockEnum>.self)
+      ]}
     }
     let object: JSONObject = ["size": NSNull()]
 
@@ -419,16 +421,15 @@ class GraphQLExecutor_SelectionSetMapper_FromResponse_Tests: XCTestCase {
     class GivenSelectionSet: MockSelectionSet {
       override class var selections: [Selection] { [Selection.field("favorites", [String].self)] }
     }
-    let object: JSONObject = ["favorites": [10, 20.0, 30]]
+    let object: JSONObject = ["favorites": [10.0, 20.0, 30]]
 
     // when
     XCTAssertThrowsError(try readValues(GivenSelectionSet.self, from: object)) { (error) in
       // then
       if let error = error as? GraphQLResultError,
          case JSONDecodingError.couldNotConvert(let value, let expectedType) = error.underlying {
-        XCTAssertEqual(error.path, ["favorites", "1"])
-        #warning("Does this need the index 1 path?")
-        XCTAssertEqual(value as? Double, 4.0)
+        XCTAssertEqual(error.path, ["favorites", "0"])
+        XCTAssertEqual(value as? Double, 10.0)
         XCTAssertTrue(expectedType == String.self)
       } else {
         XCTFail("Unexpected error: \(error)")
@@ -518,15 +519,14 @@ class GraphQLExecutor_SelectionSetMapper_FromResponse_Tests: XCTestCase {
     class GivenSelectionSet: MockSelectionSet {
       override class var selections: [Selection] { [Selection.field("favorites", [String]?.self)] }
     }
-    let object: JSONObject = ["favorites": [10, 20.0, 30]]
+    let object: JSONObject = ["favorites": [4.0, 20.0, 30]]
 
     // when
     XCTAssertThrowsError(try readValues(GivenSelectionSet.self, from: object)) { (error) in
       // then
       if let error = error as? GraphQLResultError,
          case JSONDecodingError.couldNotConvert(let value, let expectedType) = error.underlying {
-        XCTAssertEqual(error.path, ["favorites", "1"])
-        #warning("Does this need the index 1 path?")
+        XCTAssertEqual(error.path, ["favorites", "0"])
         XCTAssertEqual(value as? Double, 4.0)
         XCTAssertTrue(expectedType == String.self)
       } else {