dfa: assume fields used before initialization are null (IDEA-110297)

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

@@ -0,0 +1,14 @@
+class Foo {
+  String field;
+  String field2 = field.<warning descr="Method invocation 'substring' may produce 'java.lang.NullPointerException'">substring</warning>(1);
+  int field3 = field2.length();
+  Runnable r = new Runnable() {
+    public void run() {
+      System.out.println(field.hashCode());
+    }
+  };
+
+  Foo() {
+    field = "x";
+  }
+}

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

@@ -1,7 +1,7 @@
 class Foo {
   String field;
   String field2;
-  int hash = field.hashCode();
+  int hash = field.<warning descr="Method invocation 'hashCode' may produce 'java.lang.NullPointerException'">hashCode</warning>();
 
   Foo(String f2) {
     field2 = f2;

java/java-tests/testSrc/com/intellij/codeInspection/DataFlowInspectionTest.java

@@ -421,6 +421,8 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
 
   public void testDivisionByZero() { doTestReportConstantReferences(); }
 
+  public void testFieldUsedBeforeInitialization() { doTest(); }
+
   public void testImplicitlyInitializedField() {
     PlatformTestUtil.registerExtension(ImplicitUsageProvider.EP_NAME, new ImplicitUsageProvider() {
       @Override