Closes #2045 by allowing z_sendmany with 0 fee

src/wallet/asyncrpcoperation_sendmany.cpp

@@ -55,7 +55,7 @@ AsyncRPCOperation_sendmany::AsyncRPCOperation_sendmany(
         Value contextInfo) :
         fromaddress_(fromAddress), t_outputs_(tOutputs), z_outputs_(zOutputs), mindepth_(minDepth), fee_(fee), contextinfo_(contextInfo)
 {
-    assert(fee_ > 0);
+    assert(fee_ >= 0);
 
     if (minDepth < 0) {
         throw JSONRPCError(RPC_INVALID_PARAMETER, "Minconf cannot be negative");

src/wallet/rpcwallet.cpp

@@ -3383,7 +3383,12 @@ Value z_sendmany(const Array& params, bool fHelp)
     // Fee in Zatoshis, not currency format)
     CAmount nFee = ASYNC_RPC_OPERATION_DEFAULT_MINERS_FEE;
     if (params.size() > 3) {
-        nFee = AmountFromValue( params[3] );
+        if (params[3].get_real() == 0.0) {
+            nFee = 0;
+        } else {
+            nFee = AmountFromValue( params[3] );
+        }
+
         // Check that the user specified fee is sane.
         if (nFee > nTotalOut) {
             throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Fee %s is greater than the sum of outputs %s", FormatMoney(nFee), FormatMoney(nTotalOut)));