fix: correctly handle missing GraphQLError location/path on decode

Author: Garrett Moseke

Sources/GraphQL/Error/GraphQLError.swift

@@ -28,7 +28,7 @@ public struct GraphQLError: Error, Codable {
      *
      * Appears in the result of `description`.
      */
-    public let locations: [SourceLocation]
+    public let locations: [SourceLocation]?
 
     /**
      * An array describing the index path into the execution response which
@@ -118,7 +118,7 @@ public struct GraphQLError: Error, Codable {
     public init(from decoder: Decoder) throws {
         let container = try decoder.container(keyedBy: CodingKeys.self)
         message = try container.decode(String.self, forKey: .message)
-        locations = try container.decode([SourceLocation]?.self, forKey: .locations) ?? []
+        locations = (try? container.decode([SourceLocation]?.self, forKey: .locations)) ?? []
         path = try container.decode(IndexPath.self, forKey: .path)
     }
 
@@ -127,7 +127,7 @@ public struct GraphQLError: Error, Codable {
 
         try container.encode(message, forKey: .message)
 
-        if !locations.isEmpty {
+        if !(locations?.isEmpty ?? true) {
             try container.encode(locations, forKey: .locations)
         }
 
@@ -166,7 +166,7 @@ public struct IndexPath: Codable {
 
     public init(from decoder: Decoder) throws {
         var container = try decoder.unkeyedContainer()
-        elements = try container.decode([IndexPathValue].self)
+        elements = (try? container.decode([IndexPathValue].self)) ?? []
     }
 
     public func encode(to encoder: Encoder) throws {