Cannot moq 'Execute' after mocking 'QuerySingle<int>'

[Abinaya-Krishnan]

I want to mock both QuerySingle and Execute functions. Mocking 'Execute' after QuerySingle throws error. The error says

Message:

• System.NullReferenceException : Object reference not set to an instance of an object.

Stack Trace:

• SqlMapper.QueryRowImpl[T](IDbConnection cnn, Row row, CommandDefinition& command, Type effectiveType) line 1180

• SqlMapper.QuerySingle[T](IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Nullable1 commandTimeout, Nullable1 commandType) line 785

• SqlMapper.QuerySingle(IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Nullable1 commandTimeout, Nullable1 commandType) line 691

Please see the following example:
var moqConnection = new Mock();
const int expected = -44;

moqConnection.SetupDapper(c => c.QuerySingle("yyy", null, null, null, null)).Returns(-4);
moqConnection.SetupDapper(c => c.Execute("zzz", null, null, null, null)).Returns(-44);

var actual1 = moqConnection.Object.QuerySingle("yyy");
var actual2 = moqConnection.Object.Execute("zzz");

In the above example, if I swap 'QuerySingle' and 'Execute' then the code works.