Handle empty inputs for JSON better

We now return `null` instead of throwing an exception
if we attempt to read from an inputstream that doesn't
have any JSON content.

Author: shs96c

java/client/src/org/openqa/selenium/json/JsonInput.java

@@ -286,6 +286,13 @@ public void skipValue() {
   }
 
   public <T> T read(Type type) {
+    skipWhitespace(input);
+
+    // Guard against reading an empty stream
+    if (input.peek() == Input.EOF) {
+      return null;
+    }
+
     return coercer.coerce(this, type, setter);
   }
 

java/client/test/org/openqa/selenium/json/JsonInputTest.java

@@ -17,6 +17,7 @@
 
 package org.openqa.selenium.json;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.openqa.selenium.json.Json.MAP_TYPE;
@@ -35,7 +36,13 @@
 import org.junit.experimental.categories.Category;
 import org.openqa.selenium.testing.UnitTests;
 
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
 import java.io.StringReader;
+import java.nio.charset.StandardCharsets;
 import java.util.Map;
 import java.util.Random;
 import java.util.stream.Collectors;
@@ -258,6 +265,30 @@ public void shouldBeAbleToReadNonWellFormedDataLongerThanReadBuffer() {
         raw, raw.substring(raw.length() - 128)));
   }
 
+  @Test
+  public void nullInputsShouldCoerceAsNullValues() throws IOException {
+    try (InputStream is = new ByteArrayInputStream(new byte[0]);
+         Reader reader = new InputStreamReader(is, UTF_8);
+         JsonInput input = new Json().newInput(reader)) {
+
+      Object value = input.read(MAP_TYPE);
+
+      assertThat(value).isNull();
+    }
+  }
+
+  @Test
+  public void emptyStringsWithNoJsonValuesComeBackAsNull() throws IOException {
+    try (InputStream is = new ByteArrayInputStream("     ".getBytes(UTF_8));
+         Reader reader = new InputStreamReader(is, UTF_8);
+         JsonInput input = new Json().newInput(reader)) {
+
+      Object value = input.read(String.class);
+
+      assertThat(value).isNull();
+    }
+  }
+
   private JsonInput newInput(String raw) {
     StringReader reader = new StringReader(raw);
     return new JsonInput(reader, new JsonTypeCoercer(), BY_NAME);