Three Alternatives I found and worked:
First Alternative: Different Shaders
Use a different shader for objects with speculative and diffuse texture, and another shader for objects with only the diffuse texture.
Perhaps it is the best alternative if there is no need to create a realistic scene, that is, without the texture speculating on some objects. In addition to making graphic processing more robust.
Obs: Not all real-life materials have significant speculative behavior.
Second Alternative: Use Diffuse Texture as Specular
During the time of binding the textures you can check if the object has some speculative texture, if it does not, vincule the diffuse textures with the name of the speculative textures.
In this option you will simulate a speculative lighting. It will not result in something realistic but will not generate defects in lighting.
Obs: As in most speculative textures are obtained from the diffuse, it is possible to convert the diffuse image into gray tones to use as speculation.
Third Alternative: Change the object
Using Blender, Maia, 3Ds Max, or any other editor, you can import the object, add a speculative texture (reusing the same mapping) and export the edited object
It is the most correct option if you want to ensure that all objects have speculative texture.
Below an example by adding the speculative texture to the object using Blender.