Remove redundant assertions.

Runtime/rendering/wrap.cs

             TextDirection? textDirection = null,
             VerticalDirection verticalDirection = VerticalDirection.down
         ) {
-            D.assert(direction != null);
-            D.assert(alignment != null);
-            D.assert(spacing != null);
-            D.assert(runAlignment != null);
-            D.assert(runSpacing != null);
-            D.assert(crossAxisAlignment != null);
-
             this._direction = direction;
             this._alignment = alignment;
             this._spacing = spacing;
         public Axis direction {
             get { return this._direction; }
             set {
-                D.assert(value != null);
                 if (this._direction == value) {
                     return;
                 }
         public WrapAlignment alignment {
             get { return this._alignment; }
             set {
-                D.assert(value != null);
                 if (this._alignment == value) {
                     return;
                 }
         public float spacing {
             get { return this._spacing; }
             set {
-                D.assert(value != null);
                 if (this._spacing == value) {
                     return;
                 }
         public WrapAlignment runAlignment {
             get { return this._runAlignment; }
             set {
-                D.assert(value != null);
                 if (this._runAlignment == value) {
                     return;
                 }
         public float runSpacing {
             get { return this._runSpacing; }
             set {
-                D.assert(value != null);
                 if (this._runSpacing == value) {
                     return;
                 }
         public WrapCrossAlignment crossAxisAlignment {
             get { return this._crossAxisAlignment; }
             set {
-                D.assert(value != null);
                 if (this._crossAxisAlignment == value) {
                     return;
                 }
 
         public bool _debugHasNecessaryDirections {
             get {
-                D.assert(this.direction != null);
-                D.assert(this.alignment != null);
-                D.assert(this.runAlignment != null);
-                D.assert(this.crossAxisAlignment != null);
                 if (this.firstChild != null && this.lastChild != this.firstChild) {
                     // i.e. there"s more than one child
                     switch (this.direction) {
                             break;
                         case Axis.vertical:
-                            D.assert(this.verticalDirection != null,
-                                "Vertical $runtimeType with multiple children has a null verticalDirection, so the layout order is undefined.");
                             break;
                     }
                 }
                                 "Horizontal $runtimeType with alignment $alignment has a null textDirection, so the alignment cannot be resolved.");
                             break;
                         case Axis.vertical:
-                            D.assert(this.verticalDirection != null,
-                                "Vertical $runtimeType with alignment $alignment has a null verticalDirection, so the alignment cannot be resolved.");
                             break;
                     }
                 }
                         case Axis.horizontal:
-                            D.assert(this.verticalDirection != null,
-                                "Horizontal $runtimeType with runAlignment $runAlignment has a null verticalDirection, so the alignment cannot be resolved.");
                             break;
                         case Axis.vertical:
                             D.assert(this.textDirection != null,
                     this.crossAxisAlignment == WrapCrossAlignment.end) {
                     switch (this.direction) {
                         case Axis.horizontal:
-                            D.assert(this.verticalDirection != null,
-                                "Horizontal $runtimeType with crossAxisAlignment $crossAxisAlignment has a null verticalDirection, so the alignment cannot be resolved.");
                             break;
                         case Axis.vertical:
                             D.assert(this.textDirection != null,
             }
 
             D.assert(childConstraints != null);
-            D.assert(mainAxisLimit != null);
             float spacing = this.spacing;
             float runSpacing = this.runSpacing;
             List<_RunMetrics> runMetrics = new List<_RunMetrics> { };

Runtime/widgets/transitions.cs

             Animation<float> sizeFactor = null,
             float axisAlignment = 0.0f,
             Widget child = null) : base(key: key, listenable: sizeFactor) {
-            D.assert(axis != null);
-            D.assert(axisAlignment != null);
             this.axis = axis;
             this.axisAlignment = axisAlignment;
             this.child = child;