problem: Proxy doesn't render internal exceptions to JSON RPC errors

src/test/groovy/io/emeraldpay/dshackle/proxy/WriteRpcJsonSpec.groovy

@@ -16,10 +16,8 @@
  */
 package io.emeraldpay.dshackle.proxy
 
-import com.google.protobuf.ByteString
-import io.emeraldpay.api.proto.BlockchainOuterClass
 import io.emeraldpay.dshackle.rpc.NativeCall
-import io.emeraldpay.dshackle.test.TestingCommons
+import org.jetbrains.annotations.NotNull
 import reactor.core.publisher.Flux
 import spock.lang.Specification
 
@@ -143,4 +141,27 @@ class WriteRpcJsonSpec extends Specification {
         act[1] == '{"jsonrpc":"2.0","id":11,"error":{"code":-32002,"message":"oops"}}'
         act[2] == '{"jsonrpc":"2.0","id":15,"result":{"hash": "0x2484f459dc"}}'
     }
+
+    def "Write JSON RPC error on exception"() {
+        setup:
+        def writer = new WriteRpcJson() {
+            @Override
+            String toJson(@NotNull ProxyCall call, @NotNull NativeCall.CallResult response) {
+                throw new NativeCall.CallFailure(1, new IllegalStateException("TEST"))
+            }
+        }
+
+        def call = new ProxyCall(ProxyCall.RpcType.SINGLE)
+        call.ids[1] = 10
+        def data = [
+                new NativeCall.CallResult(1, '"0x1"'.bytes, null),
+        ]
+        when:
+        def act = Flux.fromIterable(data)
+                .transform(writer.toJsons(call))
+                .collectList()
+                .block(Duration.ofSeconds(1))
+        then:
+        act[0] == '{"jsonrpc":"2.0","id":10,"error":{"code":-32003,"message":"TEST"}}'
+    }
 }