Parsing of wind values crashes when wind duct is missing
in 'weather.py' file, 'weather_from_dictionary' function:

    # -- wind
    if 'wind' in d:
        wind = d['wind'].copy()
    elif 'last' in d:
        if 'wind' in d['last']:
            wind = d['last']['wind'].copy()

gives:

File "C:\\Python27\\lib\\site-packages\\pyowm\\webapi25\\weather.py", line 464, in weather_from_dictionary
    wind = d['wind'].copy()
AttributeError: 'NoneType' object has no attribute 'copy'

when wind dict is None

Broadly speaking, we should check that _all_ provided dicts are not None before trying to copy/manipulate them.

diff --git a/pyowm/webapi25/weather.py b/pyowm/webapi25/weather.py
index 0e22675..1fac0e7 100644
--- a/pyowm/webapi25/weather.py
+++ b/pyowm/webapi25/weather.py
@@ -458,7 +458,7 @@ def weather_from_dictionary(d):
     else:
         rain = dict()
     # -- wind
-    if 'wind' in d:
+    if 'wind' in d and d['wind'] is not None:
         wind = d['wind'].copy()
     elif 'last' in d:
         if 'wind' in d['last']:
['pyowm/webapi25/weather.py']