[Qgis-user] Rule based styling issue

[David Addy]

I have a query about the use of Rule based styles.
I have a layer of parishes within a county area, which is  styled with a
transparent fill. Below it I have a copy layer of the same data.
In both layers the attribute table has a column headed WAPENTAKE, which
holds string data of 25 characters wide. Some of the fields contain a
wapentake name, and the remainder contain NULL.
I want the copy layer to display a certain style when the wapentake contains
a name, but nothing when the column wapentake contains NULL.

Now comes the problem. If I set the copy layer to a rule based style so that
it will display a coloured shading where there is data in the field
WAPENTAKE, I expect to use the filter of "WAPENTAKE" IS NOT NULL.
This works correctly if I double click on the filter section in the Style
window, and manually edit the filter to this expression.
If instead I open the ellepsis button (...) in order to use the Expression
builder to build the same expression, the result is the reverse of what I
want.  IE those with NULL content now show the selected style, and those
that have names in the column show no style.
Can anybody shed light on this issue please? What I am I doing wrong?

(I am using QGIS 2.8.3 under Windows 7 Professional, 64 bit)



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