Java: Improve NullGuards.clearlyNotNullExpr()

java/ql/src/semmle/code/java/dataflow/NullGuards.qll

@@ -44,20 +44,22 @@ Expr clearlyNotNullExpr(Expr reason) {
   or
   result instanceof ArrayCreationExpr and reason = result
   or
+  result instanceof FunctionalExpr and reason = result
+  or
   result instanceof TypeLiteral and reason = result
   or
   result instanceof ThisAccess and reason = result
   or
   result instanceof StringLiteral and reason = result
   or
+  // Add and AssignAdd performing String concatenation never have null result
   result instanceof AddExpr and result.getType() instanceof TypeString and reason = result
   or
-  exists(Field f |
-    result = f.getAnAccess() and
-    (f.hasName("TRUE") or f.hasName("FALSE")) and
-    f.getDeclaringType().hasQualifiedName("java.lang", "Boolean") and
-    reason = result
-  )
+  result instanceof AssignAddExpr and result.getType() instanceof TypeString and reason = result
+  or
+  result.getType() instanceof PrimitiveType and reason = result
+  or
+  result instanceof CompileTimeConstantExpr and reason = result
   or
   result.(CastExpr).getExpr() = clearlyNotNullExpr(reason)
   or
@@ -70,6 +72,11 @@ Expr clearlyNotNullExpr(Expr reason) {
     (reason = r1 or reason = r2)
   )
   or
+  exists(SwitchExpr s |
+    s = result and
+    forall(Expr resultExpr | resultExpr = s.getAResult() | resultExpr = clearlyNotNullExpr(reason))
+  )
+  or
   exists(SsaVariable v, boolean branch, RValue rval, Guard guard |
     guard = directNullGuard(v, branch, false) and
     guard.controls(rval.getBasicBlock(), branch) and