Remove needless argument checks from gaia

[eerovaher]

astroquery.gaia.GaiaClass contained a handful of needless argument checks:

• In load_data() separately checking for retrieval_type being None (its default value is "ALL") is not needed because the value is checked later on, unless avoid_datatype_check is explicitly set to True:

  astroquery/astroquery/gaia/core.py

  Lines 245 to 250 in 03c8420

  	if avoid_datatype_check is False:
  	# we need to check params
  	rt = str(retrieval_type).upper()
  	if rt != 'ALL' and rt not in self.VALID_DATALINK_RETRIEVAL_TYPES:
  	raise ValueError(f"Invalid mandatory argument 'retrieval_type'. Found {retrieval_type}, "
  	f"expected: 'ALL' or any of {self.VALID_DATALINK_RETRIEVAL_TYPES}")

• In load_data() checking for ids being None only makes a difference if None is the explicitly specified value, but any other possible invalid value would pass this check, so it is not very useful.
• In cross_match() several arguments were given default values and the code then checked if any of those arguments had the default value. It is better to not specify the default value at all and to let Python itself ensure that the mandatory argument values are specified. This is not only simpler but also ensures that the error message contains the correct argument name, and if multiple arguments are missing then Python's error message makes that clear too.

[codecov]

Codecov Report

Merging #2682 (df3b6fc) into main (03c8420) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2682      +/-   ##
==========================================
- Coverage   69.19%   69.18%   -0.01%     
==========================================
  Files         304      304              
  Lines       22539    22529      -10     
==========================================
- Hits        15595    15587       -8     
+ Misses       6944     6942       -2     

Impacted Files	Coverage Δ
astroquery/gaia/core.py	70.77% <100.00%> (-0.32%)	⬇️

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[bsipocz]

Thanks @eerovaher, these all look great!

[bsipocz]

yes, I suppose we could have kept these positional args, but I think there is no need to change them now.