Remove Json::ParseError assignment (#402)

The constant was copied over from grape when grape_entity/json.rb
was introduced, but grape-entity never parses JSON and so never
used it. Because the main grape gem also defines JSON::ParseError,
loading both gems produced `already initialized constant` warnings.

Dropping the assignment silences the warnings with no behavior
change. Originally flagged in #385 by @ericproulx.

Author: olivier-thatch

CHANGELOG.md

@@ -7,7 +7,7 @@
 #### Fixes
 
 * Your contribution here.
-
+* [#402](https://github.com/ruby-grape/grape-entity/pull/402): Remove `Json::ParseError` assignment - [@olivier-thatch](https://github.com/olivier-thatch).
 
 ### 1.0.3 (2026-04-15)
 

lib/grape_entity/json.rb

@@ -2,11 +2,6 @@
 
 module Grape
   class Entity
-    if defined?(::MultiJson)
-      Json = ::MultiJson
-    else
-      Json = ::JSON
-      Json::ParseError = Json::ParserError
-    end
+    Json = defined?(::MultiJson) ? ::MultiJson : ::JSON
   end
 end