Protect against NullPointerException when using getCapabilities. (#1094)

The WebDriver capabilities field remains as null until the new-session command
succeeds, returning the capabilities stated by the server.

If an exception happens during session creation, some handling code may try to
convert the WebDriver instance to string.  In which case, the conversion would
throw a NullPointerException, masking the real failure.

This change just protects against the NullPointerException, so the real session
initiation failures can be easily troubleshooted.

Author: etanol

src/main/java/io/appium/java_client/DefaultGenericMobileDriver.java

@@ -157,7 +157,8 @@ public List findElementsByXPath(String using) {
 
     @Override
     public String toString() {
+        Capabilities capabilities = getCapabilities();
         return String.format("%s, Capabilities: %s", getClass().getCanonicalName(),
-                getCapabilities().asMap().toString());
+                capabilities != null ? capabilities.asMap().toString() : "null");
     }
 }

src/main/java/io/appium/java_client/android/AndroidDriver.java

@@ -47,6 +47,7 @@
 import java.net.URL;
 import java.util.Collections;
 import java.util.Map;
+import javax.annotation.Nullable;
 
 /**
  * Android driver implementation.
@@ -206,9 +207,12 @@ public AndroidBatteryInfo getBatteryInfo() {
      *
      * @return given {@link Capabilities}
      */
+    @Nullable
     public Capabilities getCapabilities() {
         MutableCapabilities capabilities = (MutableCapabilities) super.getCapabilities();
-        capabilities.setCapability(PLATFORM_NAME, ANDROID_PLATFORM);
+        if (capabilities != null) {
+            capabilities.setCapability(PLATFORM_NAME, ANDROID_PLATFORM);
+        }
         return capabilities;
     }
 

src/main/java/io/appium/java_client/ios/IOSDriver.java

@@ -48,6 +48,7 @@
 import java.time.Duration;
 import java.util.Collections;
 import java.util.Map;
+import javax.annotation.Nullable;
 
 /**
  * iOS driver implementation.
@@ -207,9 +208,12 @@ private class InnerTargetLocator extends RemoteTargetLocator {
      *
      * @return given {@link Capabilities}
      */
+    @Nullable
     public Capabilities getCapabilities() {
         MutableCapabilities capabilities = (MutableCapabilities) super.getCapabilities();
-        capabilities.setCapability(PLATFORM_NAME, IOS_PLATFORM);
+        if (capabilities != null) {
+            capabilities.setCapability(PLATFORM_NAME, IOS_PLATFORM);
+        }
         return capabilities;
     }