it actually works

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PropagateEmptyRelation.scala

@@ -43,7 +43,7 @@ object PropagateEmptyRelation extends Rule[LogicalPlan] with PredicateHelper {
 
   // Construct a project list from plan's output, while the value is always NULL.
   private def nullValueProjectList(plan: LogicalPlan): Seq[NamedExpression] =
-    plan.output.map{ a => Alias(Cast(Literal(null), a.dataType), a.name)(a.exprId) }
+    plan.output.map{ a => Alias(Literal(null), a.name)(a.exprId) }
 
   def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
     case p: Union if p.children.forall(isEmptyLocalRelation) =>

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/PropagateEmptyRelationSuite.scala

@@ -18,6 +18,7 @@
 package org.apache.spark.sql.catalyst.optimizer
 
 import org.apache.spark.sql.Row
+import org.apache.spark.sql.catalyst.analysis.TypeCoercion
 import org.apache.spark.sql.catalyst.{CatalystTypeConverters, InternalRow}
 import org.apache.spark.sql.catalyst.dsl.expressions._
 import org.apache.spark.sql.catalyst.dsl.plans._
@@ -37,7 +38,9 @@ class PropagateEmptyRelationSuite extends PlanTest {
         ReplaceIntersectWithSemiJoin,
         PushDownPredicate,
         PruneFilters,
-        PropagateEmptyRelation) :: Nil
+        PropagateEmptyRelation,
+        CollapseProject,
+        TypeCoercion.FunctionArgumentConversion) :: Nil
   }
 
   object OptimizeWithoutPropagateEmptyRelation extends RuleExecutor[LogicalPlan] {
@@ -209,4 +212,11 @@ class PropagateEmptyRelationSuite extends PlanTest {
 
     comparePlans(optimized, correctAnswer)
   }
+
+  test("propaget empty relation keeps the plan resolved") {
+    val query = testRelation1.join(
+      LocalRelation('a.int, 'b.int), UsingJoin(FullOuter, "a" :: Nil), None)
+    val optimized = Optimize.execute(query.analyze)
+    assert(optimized.resolved)
+  }
 }