fix(webpack): apply-base-config should initialize options it will set #…

…23296 (#23368)

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## Current Behavior
<!-- This is the behavior we have today -->
The `@nx/webpack/plugin` will resolve and read webpack options from user
defined config files.
However, it does not set the env vars indicating that a task is being
run, because tasks are not being run at this stage.

This means that certain config properties are not being set by
`applyBaseConfig`.

Users' webpack configs may rely on these properties being set so they
can modify them.
When not set, this throws, meaning the graph cannot be constructed.


## Expected Behavior
<!-- This is the behavior we should expect with the changes in this PR
-->
Initialize the properties that we usually set when `applyBaseConfig` is
used.


## Related Issue(s)
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merged. -->

Fixes #23296

packages/webpack/src/plugins/nx-webpack-plugin/lib/apply-base-config.ts

@@ -197,6 +197,20 @@ function applyNxIndependentConfig(
     moduleTrace: !!options.verbose,
     usedExports: !!options.verbose,
   };
+
+  /**
+   * Initialize properties that get set when webpack is used during task execution.
+   * These properties may be used by consumers who expect them to not be undefined.
+   *
+   * When @nx/webpack/plugin resolves the config, it is not during a task, and therefore
+   * these values are not set, which can lead to errors being thrown when reading
+   * the webpack options from the resolved file.
+   */
+  config.entry ??= {};
+  config.resolve ??= {};
+  config.module ??= {};
+  config.plugins ??= [];
+  config.externals ??= [];
 }
 
 function applyNxDependentConfig(