Remove unused nulls in disposal
Remove unused nulls in disposal

rachel-fenichel/blockly,google/blockly,google/blockly,mark-friedman/blockly,google/blockly,google/blockly,google/blockly,rachel-fenichel/blockly,mark-friedman/blockly,google/blockly,picklesrus/blockly,rachel-fenichel/blockly,mark-friedman/blockly,mark-friedman/blockly,mark-friedman/blockly,mark-friedman/blockly,rachel-fenichel/blockly,picklesrus/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,google/blockly,picklesrus/blockly