Add asserts requiring BoxConstraints' parameters to be non-null (#48295)

packages/flutter/lib/src/rendering/box.dart

@@ -90,7 +90,10 @@ class BoxConstraints extends Constraints {
     this.maxWidth = double.infinity,
     this.minHeight = 0.0,
     this.maxHeight = double.infinity,
-  });
+  }) : assert (minWidth != null),
+       assert (maxWidth != null),
+       assert (minHeight != null),
+       assert (maxHeight != null);
 
   /// Creates box constraints that is respected only by the given size.
   BoxConstraints.tight(Size size)

packages/flutter/test/rendering/box_test.dart

@@ -1007,6 +1007,13 @@ void main() {
       expect(innerConstrained.localToGlobal(Offset.zero, ancestor: outerConstrained).dy, 25.0);
     });
   });
+
+  test('BoxConstraints parameters should be non-null', () {
+    expect(() => BoxConstraints(minWidth: null), throwsAssertionError);
+    expect(() => BoxConstraints(maxWidth: null), throwsAssertionError);
+    expect(() => BoxConstraints(minHeight: null), throwsAssertionError);
+    expect(() => BoxConstraints(maxHeight: null), throwsAssertionError);
+  });
 }
 
 class _DummyHitTestTarget implements HitTestTarget {