fix(mysql): gate com_stmt_execute encode on non-empty params, not non-null params

sqlx-core/src/mysql/protocol/statement/execute.rs

@@ -18,7 +18,7 @@ impl<'q> Encode<'_, Capabilities> for Execute<'q> {
         buf.push(0); // NO_CURSOR
         buf.extend(&0_u32.to_le_bytes()); // iterations (always 1): int<4>
 
-        if !self.arguments.values.is_empty() {
+        if !self.arguments.types.is_empty() {
             buf.extend(&*self.arguments.null_bitmap);
             buf.push(1); // send type to server
 

tests/mysql/mysql.rs

@@ -200,3 +200,38 @@ async fn it_caches_statements() -> anyhow::Result<()> {
 
     Ok(())
 }
+
+#[sqlx_macros::test]
+async fn it_can_bind_null_and_non_null_issue_540() -> anyhow::Result<()> {
+    let mut conn = new::<MySql>().await?;
+
+    let row = sqlx::query("SELECT ?, ?")
+        .bind(50_i32)
+        .bind(None::<i32>)
+        .fetch_one(&mut conn)
+        .await?;
+
+    let v0: Option<i32> = row.get(0);
+    let v1: Option<i32> = row.get(1);
+
+    assert_eq!(v0, Some(50));
+    assert_eq!(v1, None);
+
+    Ok(())
+}
+
+#[sqlx_macros::test]
+async fn it_can_bind_only_null_issue_540() -> anyhow::Result<()> {
+    let mut conn = new::<MySql>().await?;
+
+    let row = sqlx::query("SELECT ?")
+        .bind(None::<i32>)
+        .fetch_one(&mut conn)
+        .await?;
+
+    let v0: Option<i32> = row.get(0);
+
+    assert_eq!(v0, None);
+
+    Ok(())
+}