Adapt response handling to Zebra (#40)

This PR allows for the Zebra behavior of not having a `result` field in the RPC response on error conditions.

Reviewed-on: #40
Co-authored-by: Rene Vergara <rene@vergara.network>
Co-committed-by: Rene Vergara <rene@vergara.network>

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 
 - Modified the `makeZebraCall` function to handle errors explicitly
+- Modified the RPC response to handle missing `result` field
 
 ## [0.5.0.1]
 

src/ZcashHaskell/Types.hs

@@ -168,7 +168,7 @@ instance (FromJSON r) => FromJSON (RpcResponse r) where
     withObject "RpcResponse" $ \obj -> do
       e <- obj .:? "error"
       i <- obj .: "id"
-      r <- obj .: "result"
+      r <- obj .:? "result"
       pure $ MakeRpcResponse e i r
 
 -- | A type to model the errors from the Zcash RPC