🐛 Some toggles save `undefined` in the YAML when switched off

[shnizzedy]

When this happens, the resulting YAML is invalid:

# Set the threshold value for refining the resulting CSF segmentation tissue mask.
# The default value is 0.95.
# CSF (cerebrospinal fluid) threshold.
undefined

# Set the threshold value for refining the resulting White Matter segmentation tissue mask.
# The default value is 0.95.
# White matter threshold.
undefined

# Set the threshold value for refining the resulting Gray Matter segmentation tissue mask.
# The default value is 0.95.
# Gray matter threshold.
undefined

# Set the threshold value for the skull-stripping of the magnitude file (when using AFNI). Depending on the data, a tighter extraction may be necessary in order to prevent noisy voxels from interfering with preparing the field map.
# The default value is 0.6.
undefined

[sgiavasis]

Good catch.