Code cleanup: Simplify Optional stream processing

Use flatMap(Optional::stream) instead of filter(..isPresent).map(..get)
and avoid a redundantly nested Optional in OpReturnType.

Also replace some unnecessary stream().forEach(..) invocations on lists
in BtcWalletService, as forEach is already part of the List interface.

core/src/main/java/bisq/core/btc/wallet/BtcWalletService.java

@@ -523,10 +523,10 @@ public Transaction completePreparedBsqTx(Transaction preparedBsqTx,
             }
 
             Transaction tx = new Transaction(params);
-            preparedBsqTxInputs.stream().forEach(tx::addInput);
+            preparedBsqTxInputs.forEach(tx::addInput);
 
             if (forcedChangeValue.isZero()) {
-                preparedBsqTxOutputs.stream().forEach(tx::addOutput);
+                preparedBsqTxOutputs.forEach(tx::addOutput);
             } else {
                 //TODO test that case
                 checkArgument(preparedBsqTxOutputs.size() == 0, "preparedBsqTxOutputs.size must be null in that code branch");
@@ -598,10 +598,10 @@ private Tuple2<Integer, Integer> getNumInputs(Transaction tx) {
             } else if (ScriptPattern.isP2WPKH(connectedOutput.getScriptPubKey())) {
                 numSegwitInputs++;
             } else {
-                throw new IllegalArgumentException("Inputs should spend a P2PKH, P2PK or P2WPKH ouput");
+                throw new IllegalArgumentException("Inputs should spend a P2PKH, P2PK or P2WPKH output");
             }
         }
-        return new Tuple2(numLegacyInputs, numSegwitInputs);
+        return new Tuple2<>(numLegacyInputs, numSegwitInputs);
     }
 
 
@@ -871,7 +871,7 @@ public void doubleSpendTransaction(String txId, Runnable resultHandler, ErrorMes
                 log.debug("txToDoubleSpend no. of inputs " + txToDoubleSpend.getInputs().size());
 
                 Transaction newTransaction = new Transaction(params);
-                txToDoubleSpend.getInputs().stream().forEach(input -> {
+                txToDoubleSpend.getInputs().forEach(input -> {
                             final TransactionOutput connectedOutput = input.getConnectedOutput();
                             if (connectedOutput != null &&
                                     connectedOutput.isMine(wallet) &&
@@ -1073,8 +1073,7 @@ public Transaction getFeeEstimationTransactionForMultipleAddresses(Set<String> f
                         addressEntryOptional = findAddressEntry(address, AddressEntry.Context.ARBITRATOR);
                     return addressEntryOptional;
                 })
-                .filter(Optional::isPresent)
-                .map(Optional::get)
+                .flatMap(Optional::stream)
                 .collect(Collectors.toSet());
         if (addressEntries.isEmpty())
             throw new AddressEntryException("No Addresses for withdraw  found in our wallet");
@@ -1255,8 +1254,7 @@ private SendRequest getSendRequestForMultipleAddresses(Set<String> fromAddresses
                         addressEntryOptional = findAddressEntry(address, AddressEntry.Context.ARBITRATOR);
                     return addressEntryOptional;
                 })
-                .filter(Optional::isPresent)
-                .map(Optional::get)
+                .flatMap(Optional::stream)
                 .collect(Collectors.toSet());
         if (addressEntries.isEmpty())
             throw new AddressEntryException("No Addresses for withdraw found in our wallet");

core/src/main/java/bisq/core/dao/governance/period/CycleService.java

@@ -134,8 +134,7 @@ private Cycle getFirstCycle() {
         // We add the default values from the Param enum to our StateChangeEvent list.
         List<DaoPhase> daoPhasesWithDefaultDuration = Arrays.stream(DaoPhase.Phase.values())
                 .map(this::getPhaseWithDefaultDuration)
-                .filter(Optional::isPresent)
-                .map(Optional::get)
+                .flatMap(Optional::stream)
                 .collect(Collectors.toList());
         return new Cycle(genesisBlockHeight, ImmutableList.copyOf(daoPhasesWithDefaultDuration));
     }

core/src/main/java/bisq/core/dao/state/model/blockchain/OpReturnType.java

@@ -51,8 +51,6 @@ public enum OpReturnType implements ImmutableDaoStateModel {
     public static Optional<OpReturnType> getOpReturnType(byte type) {
         return Arrays.stream(OpReturnType.values())
                 .filter(opReturnType -> opReturnType.type == type)
-                .map(Optional::of)
-                .findAny()
-                .orElse(Optional.empty());
+                .findAny();
     }
 }