Form binding to a Map<String, Double[]> with JSP?

[Fingel]

Hey all,
Im having some issues binding a form to my command object. The field in particular is this:

Map<String, Double[]> measureMap = new LinkedHashMap();

I then populate the map with a string key, and the doubles. It is rendered as a table in the view. It works fine to display, buy trying to make the fields editable does not:

<c:forEach items="${measureMap}" var="map" varStatus="idx">
	<tr>
		<td>${map.key}</td>
		<c:forEach items="${map.value}" var="datum" varStatus="idy">
			<td><form:input value="${datum}" path="measureMap['${map.key}'][${idy.count}]" /></td>
		</c:forEach>
	</tr>
</c:forEach>

I get the following error:

org.springframework.beans.NullValueInNestedPathException: Invalid property 'measureMap[Square Footage]' of bean class [com.stuff.esm.web.sites.SiteFormBean]: Could not instantiate property type [java.lang.Double] to auto-grow nested property path: java.lang.InstantiationException: java.lang.Double

Any idea what I am doing wrong here? Thank you in advance!