iphone - CGContextFillRects: invalid context - Objective C -

i have piece of code give images color need:

    - (uiimage*)converttomask: (uiimage *) image {     uigraphicsbeginimagecontextwithoptions(image.size, no, image.scale);     cgrect imagerect = cgrectmake(0.0f, 0.0f, image.size.width, image.size.height);      cgcontextref ctx = uigraphicsgetcurrentcontext();      // draw white background (for white mask)     cgcontextsetrgbfillcolor(ctx, 1.0f, 1.0f, 1.0f, 0.9f);     cgcontextfillrect(ctx, imagerect);      // apply source image's alpha     [image drawinrect:imagerect blendmode:kcgblendmodedestinationin alpha:1.0f];      uiimage* outimage = uigraphicsgetimagefromcurrentimagecontext();      uigraphicsendimagecontext();      return outimage; } 

everything works great in first view when add detail view, gives me error (it still works):

cgcontextsetrgbfillcolor: invalid context 0x0. serious error. application, or library uses, using invalid context , thereby contributing overall degradation of system stability , reliability. notice courtesy: please fix problem. become fatal error in upcoming update.

cgcontextfillrects: invalid context 0x0. serious error. application, or library uses, using invalid context , thereby contributing overall degradation of system stability , reliability. notice courtesy: please fix problem. become fatal error in upcoming update.

any idea how rid of error?

thanks.

edit:

the action called nil image. fixed adding condition. @ipmcc comment.

    - (uiimage*)converttomask: (uiimage *) image {      if (image != nil) {          uigraphicsbeginimagecontextwithoptions(image.size, no, image.scale);         cgrect imagerect = cgrectmake(0.0f, 0.0f, image.size.width, image.size.height);          cgcontextref ctx = uigraphicsgetcurrentcontext();          // draw white background (for white mask)         cgcontextsetrgbfillcolor(ctx, 1.0f, 1.0f, 1.0f, 0.9f);         cgcontextfillrect(ctx, imagerect);          // apply source image's alpha         [image drawinrect:imagerect blendmode:kcgblendmodedestinationin alpha:1.0f];          uiimage* outimage = uigraphicsgetimagefromcurrentimagecontext();          uigraphicsendimagecontext();          return outimage;      }else{          return image;      } } 

try this: in xcode add symbolic breakpoint cgposterror. (add symbolic breakpoint, , symbol field type cgposterror)

when error happen, debugger stop code executions , can check stack of methods calls , check parameters.