fix input_decoration _layout bug (c# doesn't support null key in Dictionary while dart support Map[null] = value)

Runtime/foundation/basic_types.cs

             it.TryGetValue(key, out v);
             return v;
         }
+        
+        public static TValue getOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> it, TKey key, TValue defaultVal) {
+            TValue v = defaultVal;
+            if (key == null) {
+                return v;
+            }
+            it.TryGetValue(key, out v);
+            return v;
+        }
 
         public static T first<T>(this IList<T> it) {
             return it[0];

Runtime/material/input_decorator.cs

         _RenderDecorationLayout _layout(BoxConstraints layoutConstraints) {
             Dictionary<RenderBox, float> boxToBaseline = new Dictionary<RenderBox, float>();
             BoxConstraints boxConstraints = layoutConstraints.loosen();
-            boxToBaseline[this.prefix] = this._layoutLineBox(this.prefix, boxConstraints);
-            boxToBaseline[this.suffix] = this._layoutLineBox(this.suffix, boxConstraints);
-            boxToBaseline[this.icon] = this._layoutLineBox(this.icon, boxConstraints);
-            boxToBaseline[this.prefixIcon] = this._layoutLineBox(this.prefixIcon, boxConstraints);
-            boxToBaseline[this.suffixIcon] = this._layoutLineBox(this.suffixIcon, boxConstraints);
+            if (this.prefix != null) {
+                boxToBaseline[this.prefix] = this._layoutLineBox(this.prefix, boxConstraints);
+            }
+            if (this.suffix != null) {
+                boxToBaseline[this.suffix] = this._layoutLineBox(this.suffix, boxConstraints);
+            }
+            if (this.icon != null) {
+                boxToBaseline[this.icon] = this._layoutLineBox(this.icon, boxConstraints);
+            }
+            if (this.prefixIcon != null) {
+                boxToBaseline[this.prefixIcon] = this._layoutLineBox(this.prefixIcon, boxConstraints);
+            }
+            if (this.suffixIcon != null) {
+                boxToBaseline[this.suffixIcon] = this._layoutLineBox(this.suffixIcon, boxConstraints);
+            }
 
             float inputWidth = Math.Max(0.0f, this.constraints.maxWidth - (
                                                   _boxSize(this.icon).width
                                                   + _boxSize(this.suffix).width
                                                   + _boxSize(this.suffixIcon).width
                                                   + this.contentPadding.right));
-            boxToBaseline[this.label] = this._layoutLineBox(this.label,
-                boxConstraints.copyWith(maxWidth: inputWidth)
-            );
-            boxToBaseline[this.hint] = this._layoutLineBox(this.hint,
-                boxConstraints.copyWith(minWidth: inputWidth, maxWidth: inputWidth)
-            );
-            boxToBaseline[this.counter] = this._layoutLineBox(this.counter, boxConstraints);
+            if (this.label != null) {
+                boxToBaseline[this.label] = this._layoutLineBox(this.label,
+                    boxConstraints.copyWith(maxWidth: inputWidth)
+                );
+            }
-            boxToBaseline[this.helperError] = this._layoutLineBox(this.helperError,
-                boxConstraints.copyWith(
-                    maxWidth: Math.Max(0.0f, boxConstraints.maxWidth
-                                             - _boxSize(this.icon).width
-                                             - _boxSize(this.counter).width
-                                             - this.contentPadding.horizontal
+            if (this.hint != null) {
+                boxToBaseline[this.hint] = this._layoutLineBox(this.hint,
+                    boxConstraints.copyWith(minWidth: inputWidth, maxWidth: inputWidth)
+                );
+            }
+
+            if (this.counter != null) {
+                boxToBaseline[this.counter] = this._layoutLineBox(this.counter, boxConstraints);
+            }
+
+            if (this.helperError != null) {
+                boxToBaseline[this.helperError] = this._layoutLineBox(this.helperError,
+                    boxConstraints.copyWith(
+                        maxWidth: Math.Max(0.0f, boxConstraints.maxWidth
+                                                 - _boxSize(this.icon).width
+                                                 - _boxSize(this.counter).width
+                                                 - this.contentPadding.horizontal
+                        )
-                )
-            );
+                );
+            }
 
             float labelHeight = this.label == null
                 ? 0
                 counterHeight,
                 helperErrorHeight
             );
-            boxToBaseline[this.input] = this._layoutLineBox(this.input,
-                boxConstraints.deflate(EdgeInsets.only(
-                    top: this.contentPadding.top + topHeight,
-                    bottom: this.contentPadding.bottom + bottomHeight
-                )).copyWith(
-                    minWidth: inputWidth,
-                    maxWidth: inputWidth
-                )
-            );
+            if (this.input != null) {
+                boxToBaseline[this.input] = this._layoutLineBox(this.input,
+                    boxConstraints.deflate(EdgeInsets.only(
+                        top: this.contentPadding.top + topHeight,
+                        bottom: this.contentPadding.bottom + bottomHeight
+                    )).copyWith(
+                        minWidth: inputWidth,
+                        maxWidth: inputWidth
+                    )
+                );
+            }
 
             // The field can be occupied by a hint or by the input itself
             float hintHeight = this.hint == null ? 0 : this.hint.size.height;
-                boxToBaseline[this.input],
-                boxToBaseline[this.hint]
+                boxToBaseline.getOrDefault(this.input, 0.0f),
+                boxToBaseline.getOrDefault(this.hint, 0.0f)
             );
 
             // Calculate the amount that prefix/suffix affects height above and below
             float fixHeight = Math.Max(
-                boxToBaseline[this.prefix],
-                boxToBaseline[this.suffix]
+                boxToBaseline.getOrDefault(this.prefix, 0.0f),
+                boxToBaseline.getOrDefault(this.suffix, 0.0f)
-                prefixHeight - boxToBaseline[this.prefix],
-                suffixHeight - boxToBaseline[this.suffix]
+                prefixHeight - boxToBaseline.getOrDefault(this.prefix, 0.0f),
+                suffixHeight - boxToBaseline.getOrDefault(this.suffix, 0.0f)
             );
             float fixBelowInput = Math.Max(
                 0,
             float subtextHelperHeight = 0;
             if (this.counter != null) {
                 subtextCounterBaseline =
-                    containerHeight + subtextGap + boxToBaseline[this.counter];
+                    containerHeight + subtextGap + boxToBaseline.getOrDefault(this.counter, 0.0f);
-                    containerHeight + subtextGap + boxToBaseline[this.helperError];
+                    containerHeight + subtextGap + boxToBaseline.getOrDefault(this.helperError, 0.0f);
                 subtextHelperHeight = helperErrorHeight;
             }