diff --git a/README.md b/README.md
index 75dc9e847a858..b5577106a40ba 100644
--- a/README.md
+++ b/README.md
@@ -37,6 +37,9 @@ The `master` branch is meant to be stable. Development is normally done in separ
 [Tags](https://github.com/dashpay/dash/tags) are created to indicate new official,
 stable release versions of Dash Core.
 
+The `develop` branch is regularly built (see doc/build-*.md for instructions) and tested, but is not guaranteed to be
+completely stable.
+
 The contribution workflow is described in [CONTRIBUTING.md](CONTRIBUTING.md)
 and useful hints for developers can be found in [doc/developer-notes.md](doc/developer-notes.md).
 
diff --git a/ci/test/00_setup_env.sh b/ci/test/00_setup_env.sh
index eff442719e914..e94162dde2dcd 100755
--- a/ci/test/00_setup_env.sh
+++ b/ci/test/00_setup_env.sh
@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 # The root dir.
 # The ci system copies this folder.
-# This is where the build is done (depends and dist).
+# This is where the depends build is done.
 BASE_ROOT_DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )"/../../ >/dev/null 2>&1 && pwd )
 export BASE_ROOT_DIR
 
@@ -59,8 +59,10 @@ export CCACHE_DIR=${CCACHE_DIR:-$CACHE_DIR/ccache}
 # The depends dir.
 # This folder exists on the ci host and ci guest. Changes are propagated back and forth.
 export DEPENDS_DIR=${DEPENDS_DIR:-$BASE_ROOT_DIR/depends}
-# Folder where the build is done (bin and lib).
+# Folder where the build result is put (bin and lib).
 export BASE_OUTDIR=${BASE_OUTDIR:-$BASE_SCRATCH_DIR/out/$HOST}
+# Folder where the build is done (dist and out-of-tree build).
+export BASE_BUILD_DIR=${BASE_BUILD_DIR:-$BASE_SCRATCH_DIR/build-ci}
 export PREVIOUS_RELEASES_DIR=${PREVIOUS_RELEASES_DIR:-$BASE_ROOT_DIR/releases/$HOST}
 export SDK_URL=${SDK_URL:-https://bitcoincore.org/depends-sources/sdks}
 export DOCKER_PACKAGES=${DOCKER_PACKAGES:-build-essential libtool autotools-dev automake pkg-config bsdmainutils curl ca-certificates ccache python3 rsync git procps}
diff --git a/ci/test/04_install.sh b/ci/test/04_install.sh
index 8e25a65a510d8..68fc56036b591 100755
--- a/ci/test/04_install.sh
+++ b/ci/test/04_install.sh
@@ -18,7 +18,7 @@ if [ "$TRAVIS_OS_NAME" == "osx" ]; then
   ${CI_RETRY_EXE} pip3 install $PIP_PACKAGES
 fi
 
-mkdir -p "${BASE_SCRATCH_DIR}"
+# Create folders that are mounted into the docker
 mkdir -p "${CCACHE_DIR}"
 mkdir -p "${PREVIOUS_RELEASES_DIR}"
 
diff --git a/configure.ac b/configure.ac
index ad96a2d1e1dac..943eaf5fa5033 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1871,7 +1871,7 @@ echo "  gprof enabled       = $enable_gprof"
 echo "  werror              = $enable_werror"
 echo
 echo "  target os           = $TARGET_OS"
-echo "  build os            = $BUILD_OS"
+echo "  build os            = $build_os"
 echo
 echo "  CC                  = $CC"
 echo "  CFLAGS              = $PTHREAD_CFLAGS $CFLAGS"
diff --git a/doc/fuzzing.md b/doc/fuzzing.md
index 859c3c04b77dd..87c9127a3dcb7 100644
--- a/doc/fuzzing.md
+++ b/doc/fuzzing.md
@@ -8,7 +8,7 @@ To quickly get started fuzzing Dash Core using [libFuzzer](https://llvm.org/docs
 $ git clone https://github.com/dashpay/dash
 $ cd dash/
 $ ./autogen.sh
-$ CC=clang CXX=clang++ ./configure --enable-fuzz --with-sanitizers=address,fuzzer,undefined --enable-c++17
+$ CC=clang CXX=clang++ ./configure --enable-fuzz --with-sanitizers=address,fuzzer,undefined
 # macOS users: If you have problem with this step then make sure to read "macOS hints for
 # libFuzzer" on https://github.com/dashpay/dash/blob/develop/doc/fuzzing.md#macos-hints-for-libfuzzer
 $ make
@@ -123,7 +123,7 @@ You may also need to take care of giving the correct path for `clang` and
 Full configure that was tested on macOS Catalina with `brew` installed `llvm`:
 
 ```sh
-./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ --disable-asm --enable-c++17
+./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ --disable-asm
 ```
 
 Read the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html) for more information. This [libFuzzer tutorial](https://github.com/google/fuzzing/blob/master/tutorial/libFuzzerTutorial.md) might also be of interest.
@@ -142,7 +142,7 @@ $ make -C AFLplusplus/ source-only
 $ ./autogen.sh
 # If afl-clang-lto is not available, see
 # https://github.com/AFLplusplus/AFLplusplus#a-selecting-the-best-afl-compiler-for-instrumenting-the-target
-$ CC=$(pwd)/AFLplusplus/afl-clang-lto CXX=$(pwd)/AFLplusplus/afl-clang-lto++ ./configure --enable-fuzz --enable-c++17
+$ CC=$(pwd)/AFLplusplus/afl-clang-lto CXX=$(pwd)/AFLplusplus/afl-clang-lto++ ./configure --enable-fuzz
 $ make
 # For macOS you may need to ignore x86 compilation checks when running "make". If so,
 # try compiling using: AFL_NO_X86=1 make
@@ -169,7 +169,7 @@ $ git clone https://github.com/google/honggfuzz
 $ cd honggfuzz/
 $ make
 $ cd ..
-$ CC=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang++ ./configure --enable-fuzz --with-sanitizers=address,undefined --enable-c++17
+$ CC=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang CXX=$(pwd)/honggfuzz/hfuzz_cc/hfuzz-clang++ ./configure --enable-fuzz --with-sanitizers=address,undefined
 $ make
 $ mkdir -p inputs/
 $ FUZZ=process_message honggfuzz/honggfuzz -i inputs/ -- src/test/fuzz/fuzz
diff --git a/doc/release-notes-bitcoin-17219.md b/doc/release-notes-bitcoin-17219.md
new file mode 100644
index 0000000000000..97df9ff0119d3
--- /dev/null
+++ b/doc/release-notes-bitcoin-17219.md
@@ -0,0 +1,8 @@
+Wallet
+------
+
+
+- The wallet can create a transaction without change even when the keypool is
+  empty. Previously it failed. (#17219)
+
+
diff --git a/src/bitcoin-cli.cpp b/src/bitcoin-cli.cpp
index 9c2e0518b290e..af24fb55b8e0e 100644
--- a/src/bitcoin-cli.cpp
+++ b/src/bitcoin-cli.cpp
@@ -26,6 +26,7 @@
 #include <memory>
 #include <optional>
 #include <stdio.h>
+#include <string>
 #include <tuple>
 
 #include <event2/buffer.h>
@@ -172,7 +173,7 @@ struct HTTPReply
     std::string body;
 };
 
-static const char *http_errorstring(int code)
+static std::string http_errorstring(int code)
 {
     switch(code) {
 #if LIBEVENT_VERSION_NUMBER >= 0x02010300
diff --git a/src/core_read.cpp b/src/core_read.cpp
index cbd31f55a52db..f0232b7902573 100644
--- a/src/core_read.cpp
+++ b/src/core_read.cpp
@@ -16,6 +16,7 @@
 #include <version.h>
 
 #include <algorithm>
+#include <string>
 
 namespace {
 
@@ -31,10 +32,9 @@ opcodetype ParseOpCode(const std::string& s)
             if (op < OP_NOP && op != OP_RESERVED)
                 continue;
 
-            const char* name = GetOpName(static_cast<opcodetype>(op));
-            if (strcmp(name, "OP_UNKNOWN") == 0)
+            std::string strName = GetOpName(static_cast<opcodetype>(op));
+            if (strName == "OP_UNKNOWN")
                 continue;
-            std::string strName(name);
             mapOpNames[strName] = static_cast<opcodetype>(op);
             // Convenience: OP_ADD and just ADD are both recognized:
             if (strName.compare(0, 3, "OP_") == 0) {  // strName starts with "OP_"
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 9d4415275c65f..6f027d18be9ed 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -849,6 +849,7 @@ static UniValue getblocktemplate(const JSONRPCRequest& request)
     result.pushKV("capabilities", aCaps);
 
     UniValue aRules(UniValue::VARR);
+    aRules.push_back("csv");
     UniValue vbavailable(UniValue::VOBJ);
     for (int j = 0; j < (int)Consensus::MAX_VERSION_BITS_DEPLOYMENTS; ++j) {
         Consensus::DeploymentPos pos = Consensus::DeploymentPos(j);
diff --git a/src/script/script.cpp b/src/script/script.cpp
index 4c3f7091de2fa..900e4e7ee5eaf 100644
--- a/src/script/script.cpp
+++ b/src/script/script.cpp
@@ -6,7 +6,9 @@
 #include <script/script.h>
 #include <util/strencodings.h>
 
-const char* GetOpName(opcodetype opcode)
+#include <string>
+
+std::string GetOpName(opcodetype opcode)
 {
     switch (opcode)
     {
diff --git a/src/script/script.h b/src/script/script.h
index cdc8dd0400796..940664e9fca4a 100644
--- a/src/script/script.h
+++ b/src/script/script.h
@@ -199,7 +199,7 @@ enum opcodetype
 // Maximum value that an opcode can be
 static const unsigned int MAX_OPCODE = OP_CHECKDATASIGVERIFY;
 
-const char* GetOpName(opcodetype opcode);
+std::string GetOpName(opcodetype opcode);
 
 class scriptnum_error : public std::runtime_error
 {
diff --git a/src/script/script_error.cpp b/src/script/script_error.cpp
index 4836c9777015c..ff84b30398a98 100644
--- a/src/script/script_error.cpp
+++ b/src/script/script_error.cpp
@@ -5,7 +5,9 @@
 
 #include <script/script_error.h>
 
-const char* ScriptErrorString(const ScriptError serror)
+#include <string>
+
+std::string ScriptErrorString(const ScriptError serror)
 {
     switch (serror)
     {
diff --git a/src/script/script_error.h b/src/script/script_error.h
index b63ce4aef70b4..32afe4cd1b764 100644
--- a/src/script/script_error.h
+++ b/src/script/script_error.h
@@ -6,6 +6,8 @@
 #ifndef BITCOIN_SCRIPT_SCRIPT_ERROR_H
 #define BITCOIN_SCRIPT_SCRIPT_ERROR_H
 
+#include <string>
+
 typedef enum ScriptError_t
 {
     SCRIPT_ERR_OK = 0,
@@ -73,6 +75,6 @@ typedef enum ScriptError_t
 
 #define SCRIPT_ERR_LAST SCRIPT_ERR_ERROR_COUNT
 
-const char* ScriptErrorString(const ScriptError error);
+std::string ScriptErrorString(const ScriptError error);
 
 #endif // BITCOIN_SCRIPT_SCRIPT_ERROR_H
diff --git a/src/script/standard.cpp b/src/script/standard.cpp
index 567e24369bf4b..1ad7a79922dc1 100644
--- a/src/script/standard.cpp
+++ b/src/script/standard.cpp
@@ -8,6 +8,8 @@
 #include <pubkey.h>
 #include <script/script.h>
 
+#include <string>
+
 typedef std::vector<unsigned char> valtype;
 
 bool fAcceptDatacarrier = DEFAULT_ACCEPT_DATACARRIER;
@@ -27,7 +29,7 @@ CKeyID ToKeyID(const PKHash& key_hash)
     return CKeyID{static_cast<uint160>(key_hash)};
 }
 
-const char* GetTxnOutputType(TxoutType t)
+std::string GetTxnOutputType(TxoutType t)
 {
     switch (t)
     {
@@ -38,7 +40,7 @@ const char* GetTxnOutputType(TxoutType t)
     case TxoutType::MULTISIG: return "multisig";
     case TxoutType::NULL_DATA: return "nulldata";
     } // no default case, so the compiler can warn about missing cases
-    return nullptr;
+    assert(false);
 }
 
 static bool MatchPayToPubkey(const CScript& script, valtype& pubkey)
diff --git a/src/script/standard.h b/src/script/standard.h
index 714f00442208c..a2983bd50fa74 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -11,6 +11,8 @@
 #include <util/hash_type.h>
 
 #include <variant>
+#include <string>
+
 
 static const bool DEFAULT_ACCEPT_DATACARRIER = true;
 
@@ -103,7 +105,7 @@ using CTxDestination = std::variant<CNoDestination, PKHash, ScriptHash>;
 bool IsValidDestination(const CTxDestination& dest);
 
 /** Get the name of a TxoutType as a C string, or nullptr if unknown. */
-const char* GetTxnOutputType(TxoutType t);
+std::string GetTxnOutputType(TxoutType t);
 
 /**
  * Parse a scriptPubKey and identify script type for standard scripts. If
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
index c27ac5317b20e..415ce8a61d492 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -98,7 +98,7 @@ static ScriptErrorDesc script_errors[]={
     {SCRIPT_ERR_SIG_FINDANDDELETE, "SIG_FINDANDDELETE"},
 };
 
-static const char *FormatScriptError(ScriptError_t err)
+static std::string FormatScriptError(ScriptError_t err)
 {
     for (const auto& script_error : script_errors) {
         if (script_error.err == err) {
@@ -132,7 +132,7 @@ void DoTest(const CScript& scriptPubKey, const CScript& scriptSig, uint32_t flag
     CMutableTransaction tx = BuildSpendingTransaction(scriptSig, txCredit);
     CMutableTransaction tx2 = tx;
     BOOST_CHECK_MESSAGE(VerifyScript(scriptSig, scriptPubKey, flags, MutableTransactionSignatureChecker(&tx, 0, txCredit.vout[0].nValue), &err) == expect, message);
-    BOOST_CHECK_MESSAGE(err == scriptError, std::string(FormatScriptError(err)) + " where " + std::string(FormatScriptError((ScriptError_t)scriptError)) + " expected: " + message);
+    BOOST_CHECK_MESSAGE(err == scriptError, FormatScriptError(err) + " where " + FormatScriptError((ScriptError_t)scriptError) + " expected: " + message);
 
     // Verify that removing flags from a passing test or adding flags to a failing test does not change the result.
     for (int i = 0; i < 16; ++i) {
diff --git a/src/test/validationinterface_tests.cpp b/src/test/validationinterface_tests.cpp
index 1e935a0ba1b05..11f8c5a53ee99 100644
--- a/src/test/validationinterface_tests.cpp
+++ b/src/test/validationinterface_tests.cpp
@@ -23,7 +23,7 @@ BOOST_AUTO_TEST_CASE(unregister_validation_interface_race)
     // Start thread to generate notifications
     std::thread gen{[&] {
         const CBlock block_dummy;
-        const BlockValidationState state_dummy;
+        BlockValidationState state_dummy;
         while (generate) {
             GetMainSignals().BlockChecked(block_dummy, state_dummy);
         }
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 43cec0be5ab77..721c3af64e322 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -1583,15 +1583,15 @@ static UniValue listsinceblock(const JSONRPCRequest& request)
         },
     }.Check(request);
 
-    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
-    if (!wallet) return NullUniValue;
-    const CWallet* const pwallet = wallet.get();
+    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
+    if (!pwallet) return NullUniValue;
 
+    const CWallet& wallet = *pwallet;
     // Make sure the results are valid at least up to the most recent block
     // the user could have gotten from another RPC command prior to now
-    pwallet->BlockUntilSyncedToCurrentChain();
+    wallet.BlockUntilSyncedToCurrentChain();
 
-    LOCK(pwallet->cs_wallet);
+    LOCK(wallet.cs_wallet);
 
     std::optional<int> height;    // Height of the specified block or the common ancestor, if the block provided was in a deactivated chain.
     std::optional<int> altheight; // Height of the specified block, even if it's in a deactivated chain.
@@ -1601,9 +1601,9 @@ static UniValue listsinceblock(const JSONRPCRequest& request)
     uint256 blockId;
     if (!request.params[0].isNull() && !request.params[0].get_str().empty()) {
         blockId = ParseHashV(request.params[0], "blockhash");
-        height.emplace();
-        altheight.emplace();
-        if (!pwallet->chain().findCommonAncestor(blockId, pwallet->GetLastBlockHash(), /* ancestor out */ FoundBlock().height(*height), /* blockId out */ FoundBlock().height(*altheight))) {
+        height = int{};
+        altheight = int{};
+        if (!wallet.chain().findCommonAncestor(blockId, wallet.GetLastBlockHash(), /* ancestor out */ FoundBlock().height(*height), /* blockId out */ FoundBlock().height(*altheight))) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
         }
     }
@@ -1616,21 +1616,21 @@ static UniValue listsinceblock(const JSONRPCRequest& request)
         }
     }
 
-    if (ParseIncludeWatchonly(request.params[2], *pwallet)) {
+    if (ParseIncludeWatchonly(request.params[2], wallet)) {
         filter |= ISMINE_WATCH_ONLY;
     }
 
     bool include_removed = (request.params[3].isNull() || request.params[3].get_bool());
 
-    int depth = height ? pwallet->GetLastBlockHeight() + 1 - *height : -1;
+    int depth = height ? wallet.GetLastBlockHeight() + 1 - *height : -1;
 
     UniValue transactions(UniValue::VARR);
 
-    for (const std::pair<const uint256, CWalletTx>& pairWtx : pwallet->mapWallet) {
+    for (const std::pair<const uint256, CWalletTx>& pairWtx : wallet.mapWallet) {
         const CWalletTx& tx = pairWtx.second;
 
         if (depth == -1 || abs(tx.GetDepthInMainChain()) < depth) {
-            ListTransactions(pwallet, tx, 0, true, transactions, filter, nullptr /* filter_label */);
+            ListTransactions(&wallet, tx, 0, true, transactions, filter, nullptr /* filter_label */);
         }
     }
 
@@ -1639,15 +1639,15 @@ static UniValue listsinceblock(const JSONRPCRequest& request)
     UniValue removed(UniValue::VARR);
     while (include_removed && altheight && *altheight > *height) {
         CBlock block;
-        if (!pwallet->chain().findBlock(blockId, FoundBlock().data(block)) || block.IsNull()) {
+        if (!wallet.chain().findBlock(blockId, FoundBlock().data(block)) || block.IsNull()) {
             throw JSONRPCError(RPC_INTERNAL_ERROR, "Can't read block from disk");
         }
         for (const CTransactionRef& tx : block.vtx) {
-            auto it = pwallet->mapWallet.find(tx->GetHash());
-            if (it != pwallet->mapWallet.end()) {
+            auto it = wallet.mapWallet.find(tx->GetHash());
+            if (it != wallet.mapWallet.end()) {
                 // We want all transactions regardless of confirmation count to appear here,
                 // even negative confirmation ones, hence the big negative.
-                ListTransactions(pwallet, it->second, -100000000, true, removed, filter, nullptr /* filter_label */);
+                ListTransactions(&wallet, it->second, -100000000, true, removed, filter, nullptr /* filter_label */);
             }
         }
         blockId = block.hashPrevBlock;
@@ -1655,7 +1655,7 @@ static UniValue listsinceblock(const JSONRPCRequest& request)
     }
 
     uint256 lastblock;
-    CHECK_NONFATAL(pwallet->chain().findAncestorByHeight(pwallet->GetLastBlockHash(), pwallet->GetLastBlockHeight() + 1 - target_confirms, FoundBlock().hash(lastblock)));
+    CHECK_NONFATAL(wallet.chain().findAncestorByHeight(wallet.GetLastBlockHash(), wallet.GetLastBlockHeight() + 1 - target_confirms, FoundBlock().hash(lastblock)));
 
     UniValue ret(UniValue::VOBJ);
     ret.pushKV("transactions", transactions);