Change CChain::FindFork() to take ref

diff --git a/src/chain.cpp b/src/chain.cpp
index 958872e5..b066f0f7 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -47,10 +47,9 @@ CBlockLocator GetLocator(const CBlockIndex* index)
     return CBlockLocator{LocatorEntries(index)};
 }
 
-const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
-    if (pindex == nullptr) {
-        return nullptr;
-    }
+const CBlockIndex* CChain::FindFork(const CBlockIndex& index) const
+{
+    const auto* pindex{&index};
     if (pindex->nHeight > Height())
         pindex = pindex->GetAncestor(Height());
     while (pindex && !Contains(*pindex))
diff --git a/src/chain.h b/src/chain.h
index a2295b08..7701e926 100644
--- a/src/chain.h
+++ b/src/chain.h
@@ -440,7 +440,7 @@ public:
     void SetTip(CBlockIndex& block);
 
     /** Find the last common block between this chain and a block index entry. */
-    const CBlockIndex* FindFork(const CBlockIndex* pindex) const;
+    const CBlockIndex* FindFork(const CBlockIndex& index) const;
 
     /** Find the earliest block with timestamp equal or greater than the given time and height equal or greater than the given height. */
     CBlockIndex* FindEarliestAtLeast(int64_t nTime, int height) const;
diff --git a/src/index/base.cpp b/src/index/base.cpp
index 416137dd..bb41cc2a 100644
--- a/src/index/base.cpp
+++ b/src/index/base.cpp
@@ -166,7 +166,7 @@ static const CBlockIndex* NextSyncBlock(const CBlockIndex* const pindex_prev, CC
 
     // Since block is not in the chain, return the next block in the chain AFTER the last common ancestor.
     // Caller will be responsible for rewinding back to the common ancestor.
-    const auto* fork{chain.FindFork(pindex_prev)};
+    const auto* fork{chain.FindFork(*pindex_prev)};
     // Common ancestor must exist (genesis).
     return chain.Next(*Assert(fork));
 }
diff --git a/src/init.cpp b/src/init.cpp
index 6642c87f..aa153a27 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -2374,7 +2374,7 @@ bool StartIndexBackgroundSync(NodeContext& node)
                     LogWarning("Failed to find block manager entry for best block %s from %s, falling back to genesis for index sync",
                         summary.best_block_hash.ToString(), summary.name);
                 } else if (!index_chain.Contains(*pindex)) {
-                    pindex = index_chain.FindFork(pindex);
+                    pindex = index_chain.FindFork(*pindex);
                 }
             }
             if (!pindex) {
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 956f7066..d65b672f 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1649,11 +1649,12 @@ static RPCMethod getchaintips()
     /* Construct the output array.  */
     UniValue res(UniValue::VARR);
     for (const CBlockIndex* block : setTips) {
+        CHECK_NONFATAL(block);
         UniValue obj(UniValue::VOBJ);
         obj.pushKV("height", block->nHeight);
         obj.pushKV("hash", block->phashBlock->GetHex());
 
-        const int branchLen = block->nHeight - active_chain.FindFork(block)->nHeight;
+        const int branchLen = block->nHeight - active_chain.FindFork(*block)->nHeight;
         obj.pushKV("branchlen", branchLen);
 
         std::string status;
diff --git a/src/test/chain_tests.cpp b/src/test/chain_tests.cpp
index cf620958..966802b6 100644
--- a/src/test/chain_tests.cpp
+++ b/src/test/chain_tests.cpp
@@ -96,13 +96,13 @@ BOOST_AUTO_TEST_CASE(findfork_tests)
 
     const auto check_same{[](const CChain& chain, const auto& blocks) {
         for (const auto& block : blocks) {
-            BOOST_CHECK_EQUAL(chain.FindFork(&block), &block);
+            BOOST_CHECK_EQUAL(chain.FindFork(block), &block);
         }
     }};
 
     const auto check_fork_point{[](const CChain& chain, const auto& blocks, const CBlockIndex& fork_point) {
         for (const auto& block : blocks) {
-            BOOST_CHECK_EQUAL(chain.FindFork(&block), &fork_point);
+            BOOST_CHECK_EQUAL(chain.FindFork(block), &fork_point);
         }
     }};
 
@@ -139,7 +139,7 @@ BOOST_AUTO_TEST_CASE(findfork_tests)
 
     // Invalid test case. Mixing chains is not supported
     CBlockIndex block_on_unrelated_chain;
-    BOOST_CHECK_EQUAL(chain_long.FindFork(&block_on_unrelated_chain), nullptr);
+    BOOST_CHECK_EQUAL(chain_long.FindFork(block_on_unrelated_chain), nullptr);
 }
 
 BOOST_AUTO_TEST_CASE(chain_test)
diff --git a/src/test/fuzz/block_index_tree.cpp b/src/test/fuzz/block_index_tree.cpp
index 0e333cd6..2eac6d6b 100644
--- a/src/test/fuzz/block_index_tree.cpp
+++ b/src/test/fuzz/block_index_tree.cpp
@@ -102,7 +102,7 @@ FUZZ_TARGET(block_index_tree, .init = initialize_block_index_tree)
                     assert(best_tip);                   // Should at least return current tip
                     if (best_tip == chain.Tip()) break; // Nothing to do
                     // Rewind chain to forking point
-                    const CBlockIndex* fork = chain.FindFork(best_tip);
+                    const CBlockIndex* fork = chain.FindFork(*best_tip);
                     // If we can't go back to the fork point due to pruned data, abort this run. In reality, a pruned node would also currently just crash in this scenario.
                     // This is very unlikely to happen due to the minimum pruning threshold of 550MiB.
                     CBlockIndex* it = chain.Tip();
diff --git a/src/validation.cpp b/src/validation.cpp
index b8903e81..d57997ce 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3183,7 +3183,7 @@ bool Chainstate::ActivateBestChainStep(BlockValidationState& state, CBlockIndex*
     if (m_mempool) AssertLockHeld(m_mempool->cs);
 
     const CBlockIndex* pindexOldTip = m_chain.Tip();
-    const CBlockIndex* pindexFork = m_chain.FindFork(pindexMostWork);
+    const CBlockIndex* pindexFork = pindexMostWork ? m_chain.FindFork(*pindexMostWork) : nullptr;
 
     // Disconnect active blocks which are no longer in the best chain.
     bool fBlocksDisconnected = false;
@@ -3397,7 +3397,7 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
             } while (!m_chain.Tip() || (starting_tip && CBlockIndexWorkComparator()(m_chain.Tip(), starting_tip)));
             if (!blocks_connected) return true;
 
-            const CBlockIndex* pindexFork = m_chain.FindFork(starting_tip);
+            const CBlockIndex* pindexFork = starting_tip ? m_chain.FindFork(*starting_tip) : nullptr;
             bool still_in_ibd = m_chainman.IsInitialBlockDownload();
 
             if (was_in_ibd && !still_in_ibd) {