Cherry picking of two commits that went to 2.1 by mistake

07149dc4d0ffa67a3dd24b470f33a238cb4114e6
cypher: Make toInt() handle float strings

88c1a9a55cee9d0b0a13f62b11a34cc46573a7dc
Make math functions return null if given a null argument

o Introduce NullSafeMathFunction to simplify things
Add better error message for some problems
Merge remote-tracking branch 'upstream/2.0-maint'