FGJ-38 Throw exception if no discovery peers

If discovery is set to true but the the channel definition
in the networkconfig doesn’t contain any peers with the
 ‘discover’ role, then a NPE is thrown.
It now throws a checked ServiceDiscoveryException

Change-Id: I43da4804119dd12df364e975af303e9f617dc355
Signed-off-by: andrew-coleman <andrew_coleman@uk.ibm.com>

src/main/java/org/hyperledger/fabric/sdk/Channel.java

@@ -166,7 +166,6 @@ public class Channel implements Serializable {
     private static final String CHAINCODE_EVENTS_TAG = "CHAINCODE_EVENTS_HANDLE";
     final Collection<Orderer> orderers = Collections.synchronizedCollection(new LinkedList<>());
     private transient Map<String, Orderer> ordererEndpointMap = Collections.synchronizedMap(new HashMap<>());
-
     // Name of the channel is only meaningful to the client
     private final String name;
     private transient String toString;
@@ -384,7 +383,6 @@ private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundE
         for (Orderer orderer : orderers) {
             ordererEndpointMap.put(orderer.getEndpoint(), orderer);
         }
-
     }
 
     /**
@@ -4387,6 +4385,9 @@ public Collection<ProposalResponse> sendTransactionProposalToEndorsers(Transacti
         if (transactionProposalRequest.getChaincodeID() == null) {
             throw new InvalidArgumentException("The proposalRequest's chaincode ID is null");
         }
+        if (null == serviceDiscovery) {
+            throw new ServiceDiscoveryException("The channel is not configured with any peers with the 'discover' role");
+        }
         logger.debug(format("Channel %s sendTransactionProposalToEndorsers chaincode name: %s", name, chaincodeName));
 
         TransactionContext transactionContext = getTransactionContext(transactionProposalRequest.getUserContext());