[java] don't replace lambda with method reference when qualifier is nullable (IDEA-278691)

GitOrigin-RevId: f514b690e9e2d007c124ce2b7179af39b6131f3f

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/lambda2methodReference/beforeNullability.java

@@ -0,0 +1,13 @@
+// "Replace lambda with method reference" "false"
+class Example {
+  private void m() { }
+
+  {
+    Example e = null;
+    Runnable unusedRunnable = () -> <caret>e.m();
+  }
+  
+  interface I {
+    void n(Example e);
+  }
+}

plugins/InspectionGadgets/src/com/intellij/codeInspection/LambdaCanBeMethodReferenceInspection.java

@@ -1,7 +1,9 @@
-// Copyright 2000-2021 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+// Copyright 2000-2022 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
 package com.intellij.codeInspection;
 
+import com.intellij.codeInsight.Nullability;
 import com.intellij.codeInsight.daemon.impl.analysis.HighlightingFeature;
+import com.intellij.codeInspection.dataFlow.NullabilityUtil;
 import com.intellij.openapi.diagnostic.Attachment;
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.project.Project;
@@ -30,7 +32,6 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.Collection;
-import java.util.function.Predicate;
 
 public class LambdaCanBeMethodReferenceInspection extends AbstractBaseJavaLocalInspectionTool {
   private static final Logger LOG = Logger.getInstance(LambdaCanBeMethodReferenceInspection.class);
@@ -335,6 +336,10 @@ public class LambdaCanBeMethodReferenceInspection extends AbstractBaseJavaLocalI
         if (element instanceof PsiField && !((PsiField)element).hasModifierProperty(PsiModifier.FINAL)) {
           return true;
         }
+
+        if (NullabilityUtil.getExpressionNullability((PsiExpression)expression, true) == Nullability.NULLABLE) {
+          return true;
+        }
       }
       return false;
     };