leading_newlines_in_multiline_strings    
            
            Start multiline strings with a newline.
This rule is available as of Dart 2.8.1.
This rule has a quick fix available.
Details
Multiline strings are easier to read when they start with a newline (a newline starting a multiline string is ignored).
BAD:
var s1 = '''{
  "a": 1,
  "b": 2
}''';
GOOD:
var s1 = '''
{
  "a": 1,
  "b": 2
}''';
var s2 = '''This one-liner multiline string is ok. It usually allows to escape both ' and " in the string.''';
Usage
To enable the leading_newlines_in_multiline_strings rule,
add leading_newlines_in_multiline_strings under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - leading_newlines_in_multiline_strings