Editor crashes when I try to change the inputs

I have this json file (an experiment):

{
    "analyzers": {
        "analyzer": {
            "algorithm": "test/iris_analyzer/1",
            "inputs": {
                "scores": "scores",
                "species": "species"
            },
            "parameters": {}
        }
    },
    "blocks": {
        "testing_alg": {
            "algorithm": "test/means_testing/1",
            "inputs": {
                "means": "measurements",
                "measurements": "lda_machine"
            },
            "outputs": {
                "scores": "scores"
            },
            "parameters": {}
        },
        "training_alg": {
            "algorithm": "test/means_training/1",
            "inputs": {
                "measurements": "measurements",
                "species": "species"
            },
            "outputs": {
                "means": "lda_machine"
            },
            "parameters": {}
        }
    },
    "datasets": {
        "testing_data": {
            "database": "iris/1",
            "protocol": "Main",
            "set": "training"
        },
        "training_data": {
            "database": "iris/1",
            "protocol": "Main",
            "set": "testing"
        }
    },
    "description": "Amir's means LDA experiment",
    "globals": {
        "environment": {
            "name": "Scientific Python 2.7",
            "version": "0.0.4"
        },
        "queue": "Default"
    }
}

When I try to edit it using the editor, it crashes with:

Traceback (most recent call last):
  File "/home/amir/miniconda/envs/beat/lib/python3.7/site-packages/beat/editor/widgets/experimenteditor.py", line 627, in __remapIO
    status, mapping = IOMapperDialog.getIOMapping(self.prefix_path, self.dump())
  File "/home/amir/miniconda/envs/beat/lib/python3.7/site-packages/beat/editor/widgets/experimenteditor.py", line 323, in getIOMapping
    return True, dialog.ioMapping()
  File "/home/amir/miniconda/envs/beat/lib/python3.7/site-packages/beat/editor/widgets/experimenteditor.py", line 301, in ioMapping
    label = self.inputs_layout.itemAt(i, QFormLayout.LabelRole).widget()
AttributeError: 'NoneType' object has no attribute 'widget'

[1]  + 120487 abort (core dumped)  beat editor start

I am trying to swap the inputs in this part:

        "testing_alg": {
            "algorithm": "test/means_testing/1",
            "inputs": {
                "means": "measurements",
                "measurements": "lda_machine"
            },

Swap means and measurements.

but when I click on save, it crashes.