I came across this error and found a solution.

Here is test code to create the problem

///////////////////////////////////////////////////
// requestImage test
PImage img;
boolean go = true;

void setup() {
size(800, 600);
}

void draw() {
if (go) {
//img = requestImage("http://192.168.0.112/DCIM/100PHOTO/SAM_0001.JPG"); // Loads the image from server successfully
img = requestImage("http://192.168.0.112/DCIM/PHOTO/SAM_0001.JPG"); // App crashes with exception
// java.lang.IllegalArgumentException: File http://192.168.0.112/DCIM/PHOTO/SAM_0001.JPG contains a path separator
go = false;
}
float ar = (float)img.width/(float)img.height;
if (img != null && img.width > 0 && img.height > 0) {
image(img, 0, 0, width, (float)width/ar);
} else {
text("Error ", width/2, height/2);
}
}
void mousePressed() {
go = true;
}
///-----------------------------------------------------------------

Process: processing.test.requestimagetest, PID: 8066
java.lang.IllegalArgumentException: File http://192.168.0.112/DCIM/PHOTO/SAM_0001.JPG contains a path separator
at android.app.ContextImpl.makeFilename(ContextImpl.java:2484)
at android.app.ContextImpl.getFileStreamPath(ContextImpl.java:699)
at android.content.ContextWrapper.getFileStreamPath(ContextWrapper.java:216)
at android.content.ContextWrapper.getFileStreamPath(ContextWrapper.java:216)
at processing.core.PSurfaceNone.getFileStreamPath(PSurfaceNone.java:319)
at processing.core.PApplet.sketchPath(PApplet.java:5506)
at processing.core.PApplet.createInputRaw(PApplet.java:5031)
at processing.core.PApplet.createInput(PApplet.java:4863)
at processing.core.PApplet.loadImage(PApplet.java:4003)
at processing.core.PApplet$AsyncImageLoader.run(PApplet.java:4076)

In PApplet.java createInputRaw() null is not returned when the file cannot be found causing expectation for non-URL filename

line 4879
/**

• Call createInput() without automatic gzip decompression.
  */
  public InputStream createInputRaw(String filename) {
  // Additional considerations for Android version:
  // http://developer.android.com/guide/topics/resources/resources-i18n.html
  InputStream stream = null;

if (filename == null) return null;

if (filename.length() == 0) {
  // an error will be called by the parent function
  //System.err.println("The filename passed to openStream() was empty.");
  return null;
}

// safe to check for this as a url first. this will prevent online
// access logs from being spammed with GET /sketchfolder/http://blahblah
if (filename.indexOf(":") != -1) {  // at least smells like URL
  try {
    // Workaround for Android bug 6066
    // http://code.google.com/p/android/issues/detail?id=6066
    // http://code.google.com/p/processing/issues/detail?id=629

// URL url = new URL(filename);
// stream = url.openStream();
// return stream;
URL url = new URL(filename);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestMethod("GET");
con.setDoInput(true);
con.connect();
return con.getInputStream();
//The following code is deprecaded by Android
// HttpGet httpRequest = null;
// httpRequest = new HttpGet(URI.create(filename));
// HttpClient httpclient = new DefaultHttpClient();
// HttpResponse response = (HttpResponse) httpclient.execute(httpRequest);
// HttpEntity entity = response.getEntity();
// return entity.getContent();
// can't use BufferedHttpEntity because it may try to allocate a byte
// buffer of the size of the download, bad when DL is 25 MB... [0200]
// BufferedHttpEntity bufHttpEntity = new BufferedHttpEntity(entity);
// return bufHttpEntity.getContent();

  } catch (MalformedURLException mfue) {
    // not a url, that's fine

**************************may need return null; // if it is really a URL it needs return null
} catch (FileNotFoundException fnfe) {
// Java 1.5 likes to throw this when URL not available. (fix for 0119)
// http://dev.processing.org/bugs/show_bug.cgi?id=403
**************************needs return null; // because this URL could not find the file, go no further
} catch (IOException e) {
// changed for 0117, shouldn't be throwing exception
printStackTrace(e);
//System.err.println("Error downloading from URL " + filename);
return null;
//throw new RuntimeException("Error downloading from URL " + filename);
}
}