Default to copying all data on transformation

As requested in code review.

python/lsst/meas/base/base.py

@@ -34,7 +34,7 @@
 
 from .baseLib import *
 from .noiseReplacer import *
-from .transforms import NullTransform
+from .transforms import PassThroughTransform
 
 # Exceptions that the measurement tasks should always propagate up to their callers
 FATAL_EXCEPTIONS = (MemoryError, FatalAlgorithmError)
@@ -274,10 +274,10 @@ def getTransformClass():
         measurement quantities to calibrated units. Calibrated data is then
         provided in a separate output table.
 
-        By default, we assume that no transformation is appropriate, and
-        therefore return NullTransform.
+        By default, we copy everything from the input to the output without
+        transformation.
         """
-        return NullTransform
+        return PassThroughTransform
 
 
 class SourceSlotConfig(lsst.pex.config.Config):

tests/testTransform.py

@@ -136,7 +136,7 @@ def testApplyCppTransform(self):
 class AlgorithmConfigurationTestCase(utilsTests.TestCase):
     def testDefaultTransform(self):
         """By default, we perform no transformations"""
-        self.assertEqual(measBase.BasePlugin.getTransformClass(), measBase.NullTransform)
+        self.assertEqual(measBase.BasePlugin.getTransformClass(), measBase.PassThroughTransform)
 
     def testWrapAlgorithm(self):
         """Test that the appropriate transform is provided for wrapped algorithms"""