Don't treat null values as zero for graduated symbology
Use isEmpty() to test for null values
Use isNull() to test for null attribute values
Consider avoid intersection settings when pasting features
30c7ec40 also applies to mingw
Fix #7195, transparency options in composer should be 0-100%
Merge pull request #453 from nyalldawson/gradfixes

Don't treat null values as zero for graduated symbology (Fix #6096)