Fix "That Wasn't Supposed to Happen" on grid Excel export (Group Attendance, Content Channel Item List)

Rock/Web/UI/Controls/Grid/Grid.cs

@@ -2444,6 +2444,15 @@ protected void Actions_ExcelExportClick( object sender, EventArgs e )
                         continue;
                     }
 
+                    // Skip indexer properties. They cannot be read without an index argument, so the
+                    // prop.GetValue( item, null ) call below would throw a TargetParameterCountException.
+                    // LavaDataObject exposes a public "this[string key]" indexer, so any grid whose data
+                    // source type inherits from it lands here.
+                    if ( prop.GetIndexParameters().Length > 0 )
+                    {
+                        continue;
+                    }
+
                     props.Add( prop );
                 }
 
@@ -2748,6 +2757,14 @@ private List<PropertyInfo> FilterDynamicObjectPropertiesCollection( Type dataSou
                     var dropProperties = typeof( RockDynamic ).GetProperties().Select( a => a.Name );
                     additionalMergeProperties = additionalMergeProperties.Where( a => !dropProperties.Contains( a.Name ) ).ToList();
                 }
+                // If this is a LavaDataObject class, don't include any of the properties that are inherited from
+                // LavaDataObject. This mirrors the non-RockLiquid branch below. Without it, LavaDataObject's
+                // "this[string key]" indexer is treated as an exportable "Item" column.
+                else if ( typeof( LavaDataObject ).IsAssignableFrom( dataSourceObjectType ) )
+                {
+                    var dropProperties = typeof( LavaDataObject ).GetProperties().Select( a => a.Name );
+                    additionalMergeProperties = additionalMergeProperties.Where( a => !dropProperties.Contains( a.Name ) ).ToList();
+                }
             }
             else
             {

Rock/Web/UI/Controls/Grid/LavaField.cs

@@ -243,7 +243,9 @@ private Dictionary<string, object> ToGridItemsDictionary( GridViewRow gridViewRo
         /// <param name="dataItem">The data item.</param>
         private void PopulateDataItemPropertiesDictionary( object dataItem )
         {
-            var dataItemProperties = dataItem.GetType().GetProperties().Where( a => a.GetGetMethod() != null && !a.GetGetMethod().IsVirtual ).ToArray();
+            // Exclude indexer properties (e.g. LavaDataObject's "this[string key]"): they cannot be read
+            // without an index argument, so GetValue( dataItem, null ) on them throws a TargetParameterCountException.
+            var dataItemProperties = dataItem.GetType().GetProperties().Where( a => a.GetGetMethod() != null && !a.GetGetMethod().IsVirtual && a.GetIndexParameters().Length == 0 ).ToArray();
             this.DataItemPropertiesDictionary = new Dictionary<string, DataFieldInfo>();
 
             // add MergeFields based on the associated ColumnHeaderText of each property of the dataitem (without spaces or special chars)