fix: check for valid ammID field in amm_info RPC (XRPLF#5188)

Author: oleks-rip

src/test/rpc/AMMInfo_test.cpp

@@ -316,13 +316,32 @@ class AMMInfo_test : public jtx::AMMTestBase
         });
     }
 
+    void
+    testInvalidAmmField()
+    {
+        using namespace jtx;
+        testcase("Invalid amm field");
+
+        testAMM([&](AMM& amm, Env&) {
+            auto const resp = amm.ammRpcInfo(
+                std::nullopt,
+                jss::validated.c_str(),
+                std::nullopt,
+                std::nullopt,
+                gw);
+            BEAST_EXPECT(
+                resp.isMember("error") && resp["error"] == "actNotFound");
+        });
+    }
+
     void
     run() override
     {
         testErrors();
         testSimpleRpc();
         testVoteAndBid();
         testFreeze();
+        testInvalidAmmField();
     }
 };
 

src/xrpld/rpc/handlers/AMMInfo.cpp

@@ -132,6 +132,8 @@ doAMMInfo(RPC::JsonContext& context)
             if (!sle)
                 return Unexpected(rpcACT_MALFORMED);
             ammID = sle->getFieldH256(sfAMMID);
+            if (ammID->isZero())
+                return Unexpected(rpcACT_NOT_FOUND);
         }
 
         if (params.isMember(jss::account))