Return hashrate of 0 when not mining. (#1672)

Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/jsonrpc/src/main/java/tech/pegasys/pantheon/ethereum/jsonrpc/internal/methods/EthHashrate.java

@@ -40,10 +40,7 @@ public class EthHashrate implements JsonRpcMethod {
   public JsonRpcResponse response(final JsonRpcRequest req) {
     try {
       final Optional<Long> hashesPerSecond = miningCoordinator.hashesPerSecond();
-      if (hashesPerSecond.isPresent()) {
-        return new JsonRpcSuccessResponse(req.getId(), Quantity.create(hashesPerSecond.get()));
-      }
-      return new JsonRpcErrorResponse(req.getId(), JsonRpcError.NO_HASHES_PER_SECOND);
+      return new JsonRpcSuccessResponse(req.getId(), Quantity.create(hashesPerSecond.orElse(0L)));
     } catch (final UnsupportedOperationException ex) {
       return new JsonRpcErrorResponse(req.getId(), JsonRpcError.INVALID_REQUEST);
     }

ethereum/jsonrpc/src/test/java/tech/pegasys/pantheon/ethereum/jsonrpc/internal/methods/EthHashrateTest.java

@@ -59,10 +59,9 @@ public class EthHashrateTest {
   }
 
   @Test
-  public void shouldReturnErrorWhenMiningCoordinatorDoesNotHaveHashes() {
+  public void shouldReturnZeroWhenMiningCoordinatorDoesNotHaveHashes() {
     final JsonRpcRequest request = requestWithParams();
-    final JsonRpcResponse expectedResponse =
-        new JsonRpcErrorResponse(request.getId(), JsonRpcError.NO_HASHES_PER_SECOND);
+    final JsonRpcResponse expectedResponse = new JsonRpcSuccessResponse(request.getId(), "0x0");
     when(miningCoordinator.hashesPerSecond()).thenReturn(Optional.empty());
 
     final JsonRpcResponse actualResponse = method.response(request);