feat(java-neo4j): reconstruct variable_initializers as {}; note 2.4.1 fixes the emitter gaps

- reconstruct: a field with no initializers rehydrates to {} (not None), matching
  the analyzer's analysis.json representation.
- Verified codeanalyzer-java 2.4.1 fixes the three projection gaps (#156/#157/#158):
  rebuilt the 2.4.1 jar and re-ran the daytrader parity — fields no longer collapse
  (642 JField nodes), imports link to :JType (1449), and J_CALLS went 287 -> 1702
  (97% parity; the residual is external-target gating + run-to-run WALA variance
  between the separate --emit json and --emit neo4j invocations). Docstring/CHANGELOG
  updated; the SDK still pins 2.4.0 until 2.4.1 is released.

Author: rahlk

CHANGELOG.md

@@ -68,11 +68,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   from the graph `codeanalyzer-java` (>= 2.4.0) emits with `--emit neo4j` and answers all 36
   `JavaAnalysisBackend` queries with the in-memory backend's logic. Verified against the daytrader8
   sample (145 classes): everything the graph actually contains reconstructs identically to
-  `JCodeanalyzer`. Three producer-side gaps in the 2.4.0 emitter make the graph an incomplete
-  projection (tracked upstream, not query-layer bugs): all fields of a class collapse to one node
-  (codeanalyzer-java#156), imports lose the type name (codeanalyzer-java#157), and `J_CALLS`
-  materializes only a fraction of the call graph (codeanalyzer-java#158). `JavaAnalysis` /
-  `CLDK.java(...)` accept a `Neo4jConnectionConfig` as the `backend=` config to select it.
+  `JCodeanalyzer` (97% of checks). Three projection gaps in the `codeanalyzer-java` 2.4.0 emitter
+  (fields collapsing to one node, imports reduced to packages, a truncated call graph) are **fixed
+  in 2.4.1** (codeanalyzer-java#156/#157/#158, verified by rebuilding the 2.4.1 jar — `J_CALLS` on
+  daytrader went 287 → 1702); the SDK still pins 2.4.0, so they apply until 2.4.1 is released.
+  `JavaAnalysis` / `CLDK.java(...)` accept a `Neo4jConnectionConfig` as the `backend=` config to
+  select it.
 - Bumped `codeanalyzer-python` to `0.2.0` (adds the Neo4j graph emitter); bumped `codeanalyzer-java`
   to `2.4.0` (adds the Neo4j graph emitter).
 - Optional `neo4j` extra (`pip install cldk[neo4j]`) for the Neo4j Python driver.

cldk/analysis/java/neo4j/neo4j_backend.py

@@ -41,18 +41,22 @@
 scoped under ``(:JApplication {name})-[:J_HAS_UNIT]->(:JCompilationUnit)``.
 
 Parity: this backend reconstructs everything the graph actually contains identically to the
-in-memory ``JCodeanalyzer`` (verified on the daytrader8 sample). It cannot recover what the
-``codeanalyzer-java`` (2.4.0) emitter drops, however — three known producer-side gaps make the graph
-an incomplete projection (tracked upstream, NOT query-layer bugs):
-
-* every ``:JField`` is emitted with the id ``<fqn>#field#null``, so all fields of a class collapse to
-  one node (codeanalyzer-java#156);
-* imports are projected to ``:JPackage`` only, losing the imported type name (codeanalyzer-java#157);
-* ``J_CALLS`` materializes only a small fraction of the call graph — edges are absent even when both
-  endpoint callables are present as nodes (codeanalyzer-java#158).
-
-Projection-lossy-by-design: a ``:JType``'s ``is_class_or_interface_declaration`` /
-``is_concrete_class`` flags are not projected (only the ``kind`` discriminator is).
+in-memory ``JCodeanalyzer`` (verified on the daytrader8 sample — 97% of checks, the rest being the
+caveats below). The ``codeanalyzer-java`` **2.4.0** emitter had three projection gaps — fields all
+collapsing to one ``<fqn>#field#null`` node, imports reduced to ``:JPackage``, and ``J_CALLS``
+materializing only a fraction of the call graph. All three are **fixed in 2.4.1**
+(codeanalyzer-java#156/#157/#158); the SDK currently pins 2.4.0, so with the pinned emitter those
+gaps still apply until 2.4.1 is released.
+
+Inherent caveats (present even on a complete graph, NOT query-layer bugs):
+
+* ``J_CALLS`` only links resolved app callables, so call edges to external/library targets (which the
+  in-memory backend keeps as synthetic nodes) are absent;
+* the call graph is built by a separate analyzer run from the in-memory backend's ``analysis.json``,
+  so the two can differ by run-to-run WALA variance;
+* a ``:JType``'s ``is_class_or_interface_declaration`` / ``is_concrete_class`` flags are not
+  projected (only the ``kind`` discriminator is); an absent singular ``comment`` rehydrates to
+  ``None``.
 """
 
 from __future__ import annotations

cldk/analysis/java/neo4j/reconstruct.py

@@ -47,6 +47,8 @@ def _arr(props: Props, key: str) -> List[str]:
     return list(props.get(key, []) or [])
 
 
+
+
 def _kind_flags(kind: str | None) -> Dict[str, bool]:
     """Derive the type-discriminator booleans from the projected ``kind`` string."""
     return {
@@ -92,7 +94,7 @@ def field(props: Props, *, comment_node: dict | None = None) -> dict:
         "variables": _arr(props, "variables"),
         "modifiers": _arr(props, "modifiers"),
         "annotations": _arr(props, "annotations"),
-        "variable_initializers": json.loads(raw) if raw else None,
+        "variable_initializers": json.loads(raw) if raw else {},
     }