bugs in load_parameter_file

[huweiATgithub]

Bug report

Required Info:

• Version or commit hash:
  

  ros2cli/ros2param/ros2param/api/__init__.py

  Lines 59 to 65 in 28d73d2

  	def get_parameter_value(*, string_value):
  	"""Guess the desired type of the parameter based on the string value."""
  	value = ParameterValue()
  	try:
  	yaml_value = yaml.safe_load(string_value)
  	except yaml.parser.ParserError:
  	yaml_value = string_value

Steps to reproduce issue

The current implementation has an extra yaml.safe_load for parameter value which has been loaded once already.
This will result in wrong results, e.g.,

key: ''

is once being loaded to {"key": ""}. Another load for the empty string "" will convert it into None.

Implementation considerations

Consider removing the extra yaml load.