Merging collapsible if statements increases the code's readability.

Noncompliant Code Example

if !filename.nil?
  if File.file?(filename) || File.directory?(filename)
    # ...
  end
end

if a then
  unless b then
    # ...
  end
end

Compliant Solution

def isFileOrDirectory(filename)
  File.file?(filename) || File.directory?(filename)
end
# ...

if !filename.nil? && isFileOrDirectory(filename)
  # ...
end

if a && !b then
  # ...
end