arcgis desktop - Raster to Numpy Array - No data values

I have several single band, 32 bit float raster datasets (fgdbr) that i want to use to build a raster stack (depth) in numpy by doing something like this dv = np.dstack((d_array, v_array))

With reference to the code snippet below,

import arcpy
d = r'P:\Sample.gdb\D_0100yr_Max'
dr  = arcpy.Raster(d)
dr.minimum # returns  0.000562695786356926
dr.maximum # returns 2.8690600395202637
dr.noDataValue # prints nothing
dr.pixelType # returns F32

d_array = arcpy.RasterToNumPyArray(dr.catalogPath, "#", "#", "#", dr.noDataValue)


d_array.max() # returns 2.86906
d_array.min() # returns -3.4028231e+38

If dr.noDataValue prints nothing, where does the RasterToNumpyArray function read the no data value from such that d_array.min() returns -3.4028231e+38 ?