matplotlib/matplotlib — pull request #1277 by bblay (2012-09-18 15:31:51+00:00)
Title: Fixed bug in MaxNLocator.bin_boundaries

```
import numpy.random
import numpy.ma as ma
import matplotlib.pyplot as plt
a = numpy.random.uniform(size=(10,10)) + 280
a2 = ma.MaskedArray(a)
plt.contour(a2) # Fails
```
```
ValueError: zero-size array to minimum.reduce without identity
```

Fixed a bug where ```MaxNLocator.bin_boundaries()``` was changing ```QuadContourSet.zmin``` and ```zmax``` in place, causing an empty levels list, and therefore the above exception.