[C#] Ast structure for CoalesceExpression

joern-cli/frontends/csharpsrc2cpg/src/main/scala/io/joern/csharpsrc2cpg/astcreation/AstForExpressionsCreator.scala

@@ -37,11 +37,19 @@ trait AstForExpressionsCreator(implicit withSchemaValidation: ValidationMode) {
       case InterpolatedStringExpression      => astForInterpolatedStringExpression(expr)
       case ConditionalAccessExpression       => astForConditionalAccessExpression(expr)
       case SuppressNullableWarningExpression => astForSuppressNullableWarningExpression(expr)
+      case CoalesceExpression                => astForCoalesceExpression(expr)
       case _: BaseLambdaExpression           => astForSimpleLambdaExpression(expr)
       case _                                 => notHandledYet(expr)
     }
   }
 
+  private def astForCoalesceExpression(coalesceExpression: DotNetNodeInfo): Seq[Ast] = {
+    val leftAst  = astForExpression(createDotNetNodeInfo(coalesceExpression.json(ParserKeys.Left)))
+    val rightAst = astForExpression(createDotNetNodeInfo(coalesceExpression.json(ParserKeys.Right)))
+
+    leftAst ++ rightAst
+  }
+
   private def astForAwaitExpression(awaitExpr: DotNetNodeInfo): Seq[Ast] = {
     /* fullName is the name in case of STATIC_DISPATCH */
     val node =

joern-cli/frontends/csharpsrc2cpg/src/main/scala/io/joern/csharpsrc2cpg/parser/DotNetJsonAst.scala

@@ -270,6 +270,8 @@ object DotNetJsonAst {
 
   object Attribute extends BaseExpr
 
+  object CoalesceExpression extends BaseExpr
+
   object Unknown extends DotNetParserNode
 
 }

joern-cli/frontends/csharpsrc2cpg/src/test/scala/io/joern/csharpsrc2cpg/querying/ast/CallTests.scala

@@ -196,4 +196,34 @@ class CallTests extends CSharpCode2CpgFixture {
     }
   }
 
+  "null-coalescing operator" should {
+    val cpg = code("""
+        |namespace Baz
+        |{
+        |    public class Foo
+        |    {
+        |        private readonly IDatabase db;
+        |
+        |        public async AnyValue GetValue(string x)
+        |        {
+        |            var value = await db.get(x) ?? new AnyValue();
+        |            return value;
+        |        }
+        |    }
+        |}
+        |""".stripMargin).moreCode("""
+        |namespace Baz;
+        |
+        |public interface IDatabase {
+        | public AnyValue get(string x) {}
+        |}
+        |""".stripMargin)
+
+    "resolve methodFullName" in {
+      inside(cpg.call.name("get").methodFullName.l) {
+        case x :: Nil => x shouldBe "Baz.IDatabase.get:AnyValue(System.String)"
+        case _        => fail("Unexpected call node structure")
+      }
+    }
+  }
 }