Rename to mapital

src/fields/color.jsx

@@ -12,7 +12,8 @@ static propTypes = {
   }
 
 	onChange(e) {
-		return this.props.onChange(e.target.value)
+		const value = e.target.value
+		return this.props.onChange(value === "" ? null: value)
 	}
 
 	render() {
@@ -22,7 +23,7 @@ static propTypes = {
 				style={inputStyle.input}
 				name={this.props.name}
 				placeholder={this.props.default}
-				value={this.props.value}
+				value={this.props.value ? this.props.value : ""}
 				onChange={this.onChange.bind(this)}
 			/>
 		</div>

src/fields/number.jsx

@@ -15,7 +15,12 @@ class NumberField extends React.Component {
   }
 
 	onChange(e) {
-		return this.props.onChange(parseFloat(e.target.value))
+		const value = parseFloat(e.target.value)
+		/*TODO: we can do range validation already here?
+		if(this.props.min && value < this.props.min) return
+		if(this.props.max && value > this.props.max) return
+		*/
+		this.props.onChange(value)
 	}
 
 	render() {

src/fields/string.jsx

@@ -12,7 +12,8 @@ static propTypes = {
   }
 
 	onChange(e) {
-		return this.props.onChange(e.target.value)
+		const value = e.target.value
+		return this.props.onChange(value === "" ? null: value)
 	}
 
 render() {