Make null param error more informative (#809)

modules/core/src/main/scala/doobie/util/put.scala

@@ -56,25 +56,37 @@ sealed abstract class Put[A](
     ) {}
 
   def unsafeSetNonNullable(ps: PreparedStatement, n: Int, a: A): Unit =
-    if (a == null) sys.error("oops, null")
-    else put.fi.apply(ps, n, (put.k(a)))
+    unsafeSetWhatShouldNotBeNull(ps, n, a, expectedNonNullableParam)
 
   def unsafeSetNullable(ps: PreparedStatement, n: Int, oa: Option[A]): Unit =
     oa match {
-      case Some(a) => unsafeSetNonNullable(ps, n, a)
+      case Some(a) => unsafeSetWhatShouldNotBeNull(ps, n, a, expectedOptionalParam)
       case None    => unsafeSetNull(ps, n)
     }
 
+  private def unsafeSetWhatShouldNotBeNull(ps: PreparedStatement, n: Int, a: A, message: String): Unit =
+    if (a == null) sys.error(message)
+    else put.fi.apply(ps, n, (put.k(a)))
+
   def unsafeUpdateNonNullable(rs: ResultSet, n: Int, a: A): Unit =
-    if (a == null) sys.error("oops, null")
-    else update.fi.apply(rs, n, (update.k(a)))
+    unsafeUpdateWhatShouldNotBeNull(rs, n, a, expectedNonNullableParam)
 
   def unsafeUpdateNullable(rs: ResultSet, n: Int, oa: Option[A]): Unit =
     oa match {
-      case Some(a) => unsafeUpdateNonNullable(rs, n, a)
+      case Some(a) => unsafeUpdateWhatShouldNotBeNull(rs, n, a, expectedOptionalParam)
       case None    => rs.updateNull(n)
     }
 
+  private def unsafeUpdateWhatShouldNotBeNull(rs: ResultSet, n: Int, a: A, message: String): Unit =
+    if (a == null) sys.error(message)
+    else update.fi.apply(rs, n, (update.k(a)))
+
+  private val expectedNonNullableParam =
+    "Expected non-nullable param. Use Option to describe nullable values."
+
+  private val expectedOptionalParam =
+    "Expected optional param but got Some(null)."
+
   override def toString(): String = {
     s"Put(typeStack=${typeStack.mkString_(",")}, jdbcTargets=${jdbcTargets.mkString_(
         ",")}, vendorTypeNames=${vendorTypeNames.mkString_(",")})"

modules/core/src/test/scala/doobie/util/WriteSuite.scala

@@ -122,4 +122,27 @@ class WriteSuite extends munit.FunSuite with WriteSuitePlatform {
       .unsafeRunSync()
   }
 
+  test("Write should yield correct error when Some(null) inserted") {
+    interceptMessage[RuntimeException]("Expected optional param but got Some(null).") {
+      testNullPut(("a", Some(null)))
+    }
+  }
+
+  test("Write should yield correct error when null inserted into non-nullable field") {
+    interceptMessage[RuntimeException]("Expected non-nullable param. Use Option to describe nullable values.") {
+      testNullPut((null, Some("b")))
+    }
+  }
+
+  private def testNullPut(input: (String, Option[String])): Int = {
+    import doobie.implicits.*
+
+    (for {
+      _ <- sql"create temp table t0 (a text, b text null)".update.run
+      n <- Update[(String, Option[String])]("insert into t0 (a, b) values (?, ?)").run(input)
+    } yield n)
+      .transact(xa)
+      .unsafeRunSync()
+  }
+
 }