conditional: treat nulls separately and accept them as numeric/boolean branches (IDEA-157025)

java/java-psi-api/src/com/intellij/psi/impl/source/resolve/graphInference/PsiPolyExpressionUtil.java

@@ -160,7 +160,7 @@ public class PsiPolyExpressionUtil {
   }
 
   private enum ConditionalKind {
-    BOOLEAN, NUMERIC
+    BOOLEAN, NUMERIC, NULL
   }
 
   private static ConditionalKind isBooleanOrNumeric(PsiExpression expr) {
@@ -192,14 +192,18 @@ public class PsiPolyExpressionUtil {
       final PsiExpression elseExpression = ((PsiConditionalExpression)expr).getElseExpression();
       final ConditionalKind thenKind = isBooleanOrNumeric(thenExpression);
       final ConditionalKind elseKind = isBooleanOrNumeric(elseExpression);
-      if (thenKind == elseKind || elseKind == null) return thenKind;
-      if (thenKind == null) return elseKind;
+      if (thenKind == elseKind || elseKind == ConditionalKind.NULL) return thenKind;
+      if (thenKind == ConditionalKind.NULL) return elseKind;
     }
     return null;
   }
 
   @Nullable
   private static ConditionalKind isBooleanOrNumericType(PsiType type) {
+    if (type == PsiType.NULL) {
+      return ConditionalKind.NULL;
+    }
+
     final PsiClass psiClass = PsiUtil.resolveClassInClassTypeOnly(type);
     if (TypeConversionUtil.isNumericType(type)) return ConditionalKind.NUMERIC;
     if (TypeConversionUtil.isBooleanType(type)) return ConditionalKind.BOOLEAN;

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/lambda/graphInference/PolyConditionalExpressionWithTargetPrimitive.java

@@ -6,6 +6,11 @@ class Conditional {
     int a2 = b ? null : 1;
     int a3 = b ? null : f1();
     int a4 = b ? null : f2();
+    Long someNum = b ? getNum(5L) : <error descr="Incompatible types. Found: 'int', required: 'java.lang.Long'">0</error>;
+  }
+
+  private static <T> T getNum(T num) {
+    return num;
   }
 
   private static <T> T f() {