Slenderman Monster

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Null objects are probably group nodes in Maya. Open your outliner (window>outliner). You should see a hierarchy of your objects in the scene. Your mesh should not be parented under anything else, if it is parented under a thing with the symbol of a red arrow on top of a white rectangle (sorry can't make screenshots right now), select the mesh and hit SHIFT + P to unparent it. Delete the now empty group. Actually there should not be anything in your scene, except for your mesh, the single joint, the four viewport cameras and two default sets that are always there (default light set and default object set. I don't know if they can even be deleted...)

Another thing you can try is delete Mayas history. This will clean up the scene and often helps with all kinds of problems. Go to Edit > Delete All by Type > Non-Deformer History to do that. (Make sure you chose non-deformer, otherwise your skinning will be deleted as well!)

Finally, a thing I found simply by copypastaing your sentence into google (minus the name of the object of course), it seems like the collada exporter has a problem with meshes that are too small. In this case, scaling up the mesh can help with the problem you're having. I don't know however if there's a way to scale it back down in the model editor.
Edit: Oh god I almost forgot - of course you need to scale the mesh before you bind it to the joint or detach it first! otherwise the scene will probably explode or something