GraphQLError: revert originalError to be nullable (#3341)

Author: IvanGoncharov

src/error/GraphQLError.d.ts

@@ -76,7 +76,7 @@ export class GraphQLError extends Error {
   /**
    * The original error thrown from a field resolver during execution.
    */
-  readonly originalError: Error | undefined;
+  readonly originalError: Error | undefined | null;
 
   /**
    * Extension fields to add to the formatted error.

src/error/GraphQLError.js

@@ -56,7 +56,7 @@ export class GraphQLError extends Error {
   /**
    * The original error thrown from a field resolver during execution.
    */
-  +originalError: Error | void;
+  +originalError: Error | void | null;
 
   /**
    * Extension fields to add to the formatted error.