dfa: handle in a special way only getX() != null comparisons (IDEA-141823)

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/DfaMemoryStateImpl.java

@@ -650,13 +650,15 @@ public class DfaMemoryStateImpl implements DfaMemoryState {
       return true;
     }
 
+    final boolean containsCalls = dfaLeft instanceof DfaVariableValue && ((DfaVariableValue)dfaLeft).containsCalls();
+    
     // track "x" property state only inside "if (getX() != null) ..."
-    if (dfaLeft instanceof DfaVariableValue && ((DfaVariableValue)dfaLeft).containsCalls() && (!isNull(dfaRight) || !isNegated)) {
+    if (containsCalls && !isNotNull(dfaLeft) && isNull(dfaRight) && !isNegated) {
       return true;
     }
     
     if (dfaLeft == dfaRight) {
-      return !isNegated;
+      return containsCalls || !isNegated;
     }
 
     if (isNull(dfaLeft) && isNotNull(dfaRight) || isNull(dfaRight) && isNotNull(dfaLeft)) {

java/java-tests/testData/inspection/dataFlow/fixture/ContractWithNullable.java

@@ -41,3 +41,21 @@ class Foo {
 
 }
 
+class Test {
+  @NotNull
+  String getName() {
+    return "";
+  }
+
+  @Nullable
+  @Contract("!null -> !null")
+  String convert(@Nullable String name) {
+    return name;
+  }
+
+
+  @NotNull
+  String test() {
+    return convert(getName());
+  }
+}