TypeError in floatToGoString in utils.py

When one PureStorage array controller is failed it reports None value for metric purefa_network_interface_performance. The function floatToGoString fails because it cannot handle None value.

I added two lines in my local copy of "utils.py" to make this function work, so it replaces None value with 0 (zero).

Instead of:

def floatToGoString(d):
   d = float(d)

I use:

def floatToGoString(d):
    if d is None:
        d = 0
    d = float(d)

Below is the error message:

File "/home/pure_exporter/venv/lib/python3.7/site-packages/prometheus_client/utils.py", line 9, in floatToGoString
d = float(d)
TypeError: ("float() argument must be a string or a number, not 'NoneType'", Metric(purefa_network_interface_performance, FlashArray network interface performance, gauge, , [Sample(name='purefa_network_interface_performance', labels={'interface': 'ct0.eth5', 'dimension': 'rx_bytes'}, value=None, timestamp=None, exemplar=None),

从 utils.py 中的 floatToGoString 开始，使用 None 值重现该失败。查看此工具周围现有的测试，然后添加回归测试，表明 None 会被作为零处理，同时普通数值输入仍能正常工作。当报告的指标可以在不出现 TypeError 的情况下序列化时，即表示完成。