[1.5.4] Fix some issues.

Runtime/gestures/binding.cs

             }
 
             HitTestResult hitTestResult = null;
-            if (evt is PointerDownEvent || evt is PointerSignalResolver) {
+            if (evt is PointerDownEvent || evt is PointerSignalEvent) {
                 D.assert(!this._hitTests.ContainsKey(evt.pointer));
                 hitTestResult = new HitTestResult();
                 this.hitTest(hitTestResult, evt.position);

Runtime/painting/continuous_rectangle_border.cs

         }
 
         public override ShapeBorder lerpFrom(ShapeBorder a, float t) {
-            D.assert(t != null);
             if (a is ContinuousRectangleBorder) {
                 return new ContinuousRectangleBorder(
                     side: BorderSide.lerp((a as ContinuousRectangleBorder).side, this.side, t),
         }
         
         public override ShapeBorder lerpTo(ShapeBorder b, float t) {
-            D.assert(t != null);
             if (b is ContinuousRectangleBorder) {
                 return new ContinuousRectangleBorder(
                     side: BorderSide.lerp(this.side, (b as ContinuousRectangleBorder).side, t),

Runtime/painting/text_painter.cs

             return this._caretMetrics.offset;
         }
 
-        public float getFullHeightForCaret(TextPosition position, Rect caretPrototype) {
+        public float? getFullHeightForCaret(TextPosition position, Rect caretPrototype) {
-            return this._caretMetrics.fullHeight ?? 0;
+            return this._caretMetrics.fullHeight;
         }
 
         _CaretMetrics _caretMetrics;

Runtime/rendering/editable.cs

                     caretRect.left,
                     caretRect.top - _kCaretHeightOffset,
                     caretRect.width,
-                    this._textPainter.getFullHeightForCaret(textPosition, this._caretPrototype)
+                    this._textPainter.getFullHeightForCaret(textPosition, this._caretPrototype).Value
                 );
             }
 #endif