Allow subclasses of Builder to determine if children are initialized.

In some unreleased versions of suds-jurko, all elements that were populated with empty lists. This was fixed in suds-commnunity as a regression, see #14, #15, and #16.

This changes allows consumers of suds to have the suds-jurko behavior by doing the following:
```
from suds.client import Client, Builder

class MyBuilder(Builder):
    def skip_value(self, type):
        return False # always set value

client = Client('...')
client.factory.builder = MyBuilder(client.factory.builder.resolver)
```

CHANGELOG.md

@@ -4,6 +4,7 @@ Release notes
 Unreleased
 ------------------------
 * Fix undeclared variables, found via linting.
+* Allow subclassing Builder to always initialize optional arrays with empty lists
 
 version 1.0.0, 1.0.0-beta.1, 1.0.0-beta.2 (2021-09-13)
 ------------------------

README.md

@@ -418,6 +418,25 @@ within the WSDL import each other.
 * username:: username for HTTP authentication.
 * password:: password for HTTP authentication.
 
+### Custom behavior through swapping components
+
+Various ways that suds behaves can be customized by swapping out custom
+
+#### Initializing optional arrays with lists
+
+In some unreleased versions of suds-jurko, all children elements were populated with empty lists. This was fixed in suds-community as a regression. This can be desired behavior as it simplifies constructing complex requests. To obtain the prior behavior, use a custom `Builder` class, for example:
+
+```
+from suds.client import Client, Builder
+
+class AlwaysInitializeBuilder(Builder):
+    def skip_value(self, type):
+        return False # always set value
+
+client = Client(url)
+client.factory.builder = AlwaysInitializeBuilder(client.factory.builder.resolver)
+```
+
 ## Enumerations
 
 Enumerations are handled as follows:

suds/builder.py

@@ -84,7 +84,7 @@ def process(self, data, type, history):
                     md.sxtype = resolved
                     md.ordering = self.ordering(resolved)
 
-        setattr(data, type.name, value if not type.optional() or type.multi_occurrence() else None)
+        setattr(data, type.name, None if self.skip_value(type) else value)
         if value is not None:
             data = value
         if not isinstance(data, list):
@@ -109,6 +109,10 @@ def skip_child(self, child, ancestry):
                 return True
         return False
 
+    def skip_value(self, type):
+        """ whether or not to skip setting the value """
+        return type.optional() and not type.multi_occurrence()
+
     def ordering(self, type):
         """ get the ordering """
         result = []