column with hflex min causes JS error in grid with footer

When at 1 or more columns in a grid receive the hflex=min property, and a footer, the following error is thrown in browser:
Uncaught TypeError: Cannot read property 'style' of undefined

This only happens if the number of footer is lower than the number of columns. (if some footer have the span property, for example)

see following example:

<zk>
<grid>
<columns>
<column label="Col 1" hflex="min" />
<column label="Col 2" hflex="1" />
<column label="Col 3" hflex="1" />
<column label="Col 4" hflex="1" />
</columns>
<rows>
<row>
<label value="1" />
<label value="2" />
<label value="3" />
<label value="4" />
</row>
</rows>
<foot>
<footer label="1" span="2"/>
<footer label="3" />
<footer label="4" />
</foot>
</grid>
</zk>