diff --git a/externs/olx.js b/externs/olx.js
index 8b073ba63a..d8ba2cbfbd 100644
--- a/externs/olx.js
+++ b/externs/olx.js
@@ -1160,7 +1160,7 @@ olx.format.ReadOptions.prototype.dataProjection;
 
 
 /**
- * Projection of the feature geometries created by the format reader. if not
+ * Projection of the feature geometries created by the format reader. If not
  * provided, features will be returned in the `dataProjection`.
  * @type {ol.proj.ProjectionLike|undefined}
  */
diff --git a/src/ol/format/featureformat.js b/src/ol/format/featureformat.js
index ff674c19c7..0627c4b90c 100644
--- a/src/ol/format/featureformat.js
+++ b/src/ol/format/featureformat.js
@@ -149,21 +149,22 @@ ol.format.Feature.transformWithOptions = function(
 
 
 /**
- * @param {(olx.format.WriteOptions|olx.format.ReadOptions)=} opt_options
+ * @param {olx.format.WriteOptions|olx.format.ReadOptions|undefined} options
  *     Options.
  * @param {ol.proj.ProjectionLike} defaultDataProjection Default projection.
  * @protected
- * @return {(olx.format.WriteOptions|olx.format.ReadOptions)=} Updated options.
+ * @return {olx.format.WriteOptions|olx.format.ReadOptions|undefined}
+ *     Updated options.
  */
 ol.format.Feature.setDefaultDataProjection = function(
-    opt_options, defaultDataProjection) {
-  if (goog.isDef(opt_options)) {
-    if (!goog.isDef(opt_options.dataProjection)) {
-      opt_options = {
-        featureProjection: opt_options.featureProjection,
+    options, defaultDataProjection) {
+  if (goog.isDef(options)) {
+    if (!goog.isDef(options.dataProjection)) {
+      options = {
+        featureProjection: options.featureProjection,
         dataProjection: defaultDataProjection
       };
     }
   }
-  return opt_options;
+  return options;
 };
diff --git a/src/ol/format/polylineformat.js b/src/ol/format/polylineformat.js
index 750f1aa078..85b357c094 100644
--- a/src/ol/format/polylineformat.js
+++ b/src/ol/format/polylineformat.js
@@ -311,7 +311,7 @@ ol.format.Polyline.prototype.readGeometryFromText =
 
   // for convenience set a default dataProjection
   opt_options = ol.format.Feature.setDefaultDataProjection(
-      opt_options, this.readProjectionFromText(null));
+      opt_options, this.readProjectionFromText(''));
 
   return ol.format.Feature.transformWithOptions(
       new ol.geom.LineString(coordinates), false, false, opt_options);
@@ -381,9 +381,10 @@ ol.format.Polyline.prototype.writeGeometryText =
   goog.asserts.assertInstanceof(geometry, ol.geom.LineString);
   // for convenience set a default dataProjection
   opt_options = ol.format.Feature.setDefaultDataProjection(
-      opt_options, this.readProjectionFromText(null));
-  geometry = ol.format.Feature.transformWithOptions(
-      geometry, true, true, opt_options);
+      opt_options, this.readProjectionFromText(''));
+  geometry = /** @type {ol.geom.LineString} */
+      (ol.format.Feature.transformWithOptions(
+          geometry, true, true, opt_options));
   var flatCoordinates = geometry.getFlatCoordinates();
   var stride = geometry.getStride();
   return ol.format.Polyline.encodeDeltas(flatCoordinates, stride, this.factor_);
diff --git a/src/ol/format/xmlfeatureformat.js b/src/ol/format/xmlfeatureformat.js
index dc185b74df..d6c23aaeb0 100644
--- a/src/ol/format/xmlfeatureformat.js
+++ b/src/ol/format/xmlfeatureformat.js
@@ -271,8 +271,11 @@ ol.format.XMLFeature.transformFeaturesWithOptions = function(
     }
 
     goog.array.forEach(features, function(feature) {
-      feature.setGeometry(ol.format.Feature.transformWithOptions(
-          feature.getGeometry(), write, false, opt_options));
+      var geom = feature.getGeometry();
+      if (goog.isDef(geom)) {
+        feature.setGeometry(ol.format.Feature.transformWithOptions(
+            geom, write, false, opt_options));
+      }
     });
   }
   return features;