False positive: "WARNING: VerifyWarning: Invalid 'BLANK' keyword in header."

[malikolivier]

How to reproduce

Load the following test FITS file containing a BLANK value set to "1" in its header (appended .txt to upload it on github):
test.mob.fits.txt

from astropy.io import fits
fits.open('test.mob.fits.txt')

The following warning will be printed.

WARNING: VerifyWarning: Invalid 'BLANK' keyword in header.  The 'BLANK' keyword is only applicable to integer data, and will be ignored in this HDU. [astropy.io.fits.hdu.image]

Expected behaviour

The FITS standard says that BLANK shall be an integer [1].
The FITS standard defines an integer as "An integer consists of a +' (hexadecimal 2B) or -' (hexadecimal 2D) sign, followed by one or more ASCII digits (hexadecimal 30 to 39), with no embedded spaces." [2]

The FITS file I attached should be compliant, as such no warning should be printed.

Versions

• Python: 3.6.3
• astropy: 3.0
• OS: Ubuntu 17.10

[1] https://heasarc.gsfc.nasa.gov/docs/fcg/standard_dict.html
[2] 5.2.3 Integer Number: http://archive.stsci.edu/fits/fits_standard/node33.html#SECTION00923000000000000000

[saimn]

As stated in the warning message, The 'BLANK' keyword is only applicable to integer data. Your data is float (BITPIX = -32), hence the warning.
Also from the FITS standard, section 5.3:

The BLANK keyword should not be used when
BITPIX = -32 or -64; rather, the IEEE NaN should be
used to represent an undefined value.